I want to have an arcane trap that cast hold person but should the PC be able to find it with a investigation check? I want it to be like invisible and when they step on the spot it activates. Is that a bit hard or should it be detectable with just a investigation check or should it be arcana since its a Arcane trap?

I would say to discover the trap trigger (pressure plate, hidden rune, etc, it would be investigation. Once discovered, to understand what the trap does once it is triggered I would call for an arcana check. Just one person’s opinion, would be curious to hear others ruling on this.

glyph of warding or just make up whatever you want =)

Quote from Crissair >>

I would say to discover the trap trigger (pressure plate, hidden rune, etc, it would be investigation. Once discovered, to understand what the trap does once it is triggered I would call for an arcana check. Just one person’s opinion, would be curious to hear others ruling on this.

Going off how Snare works. I agree with Crissair about, Investigation to discover the trap. Arcana once discovered/sprung, to understand the trap.

If its a glyph of warding, it might be visible (perception) from the method of inscribing it -probably difficult. Investigation would be more likely to find it: Hmm incense resin, odd place to meditate, ah diamond flakes in the grouting - and whats this Invoked comsumption of Keters due burn marks. Yup boys we have a glyph of warding here.

Of course how difficult you make that to noticeis another thing.

If its a magical trap and your making your own calls on how to identifiy magics? well then discovery possibility is on you. The DMG suggests fondling an item on a short rest can determine the properties of a magic item even if your an Orc barbarian with an Intelligence of 3. If thats the case then noticing a magic area being different? It seems likely for someone looking for traps and trained at some point by others to look specifically for magical traps as they are endemic in the fantasy world.

If noticing magic is difficult and magic items are harder to damage than non magical, then rogues when investigating would only need to scratch test an area to find a magically altered source.

So yes there are explanations for rogues scouting magic traps if you as a DM wish for that but at your table you should make the decision, and hopefully it will be one that reinforces and allows you to build on your game world 'science'

Have fun :)

Quote from Moondruidsneversleep >>

If its a glyph of warding, it might be visible (perception) from the method of inscribing it -probably difficult. Investigation would be more likely to find it: Hmm incense resin, odd place to meditate, ah diamond flakes in the grouting - and whats this Invoked comsumption of Keters due burn marks. Yup boys we have a glyph of warding here.

Of course how difficult you make that to noticeis another thing.

Or just go with what the glyph spell says?

The glyph is nearly invisible and requires a successful Intelligence (Investigation) check against your spell save DC to be found.

I see no reason to bother changing this and make things more complicated - it does the job perfectly fine.

Cy, the question Estevezrr asked was should they be able to. My answer wasnt about complicating it - it was offering examples of how you could find something and thats not making it complicated, thats stepping in where the phb doesnt. The dmg states that an almost impossible check - the hardest check there is, is 30. So with a skill use how could you justify what was noticed (improbably in some cases) and ta-dah we have an answer. I cant be sure but I imagine the question was about what the scout would discover - what it would look / smell / feel or taste like that would be noticeable by a check, and at that point if there is a distinction then a perception check may work as I mentioned (from the method of inscribing)

How do you describe telltales a glyph of warding to have left clues that an investigation would have revealed in your game?

Quote from Moondruidsneversleep >>

Cy, the question Estevezrr asked was should they be able to. My answer wasnt about complicating it - it was offering examples of how you could find something and thats not making it complicated, thats stepping in where the phb doesnt. The dmg states that an almost impossible check - the hardest check there is, is 30. So with a skill use how could you justify what was noticed (improbably in some cases) and ta-dah we have an answer. I cant be sure but I imagine the question was about what the scout would discover - what it would look / smell / feel or taste like that would be noticeable by a check, and at that point if there is a distinction then a perception check may work as I mentioned (from the method of inscribing)

 
They didn't ask "should", they asked "how" to make a trap and how it might be found: investigation or arcana. The answer was glyph of warding - he does precisely what he is asking for and detals how it could be found with a check. He did not ask about scouting or what would be found in terms of look smell or whatever - just how can be make a Hold Person trap with magic and how would players be able to find it if they searched. Both of these are answered by the spell Glyph of Warding which he seemed to be unaware of.

Quote from Moondruidsneversleep >>

How do you describe telltales a glyph of warding to have left clues that an investigation would have revealed in your game?

 I'd have them find the glyph. The only thing the spell leaves behind is a nearly invisible glyph. If they search (investigation) and meet the DC then the character finds the glyph and in a way that would not trigger it (which would depend on where the caster of it placed it and what triggers were placed).

You are complicating it by creating signs the glyph spell doesnt leave. The spell already includes a skill check and DC for being able to find it. The glyph isn't invisible. The spell and placement can make it harder to find but it remains findable. Seeing the glyph is more than justification enough, throwing in made-up "traces" is superfluous.

By that level of professionalism applied to spellcasting by someone, making no mistakes and leaving no trace, haveing magic clear up after itself and leaving no residual whatsoever, if applied to trapmakers and those concealing doors, nothing could be seen as no tell tales where ever left there. I maintain from what I understood there was a question, and those answering these points were losing this 'how could they be noticed?' part of the question - indeed how should I handle this?. You can run your game that way but then you might end up arbitrarily deciding or accidentally enforcing a complete renunciation of some skills as they can not ever succeed - despite even specifically asked questions which you didnt consider or uses that would note details. It doesnt have to be the case, and indeed I repeat you can run it like you say. I am more concerned with the one and done binary that is offered.

Investigation is your search skill and encompasses all you need for searching.

The Glyph of Warding spell doesn't require you to find "traces" - because you find the glyph itself. It creates a mark that you can find if your Investigation meets the DC ("if your searching was good enough").

Going into the minutiae of fine details which you have to make up (I'm going by the spell, what are you going by?) - I don't understand the point of replacing "find the glyph" with "find X trace" -- you're still rolling Investigation (the Search skill) against the spell DC. Mechanically there's no difference so what is the point of changing it?

When a party are looking for traps they roll Investigation. If they meet the DC, they find the glyph before it gets triggered. If they used the level 1 spell Detect Magic they'd either find it instantly or get advantage depending on how you wanted to run it.

The OP asks how he can set a magic trap of Hold Person and if he did how would players find this trap? We answered that you can use Glyph of Warding to set the trap and the players would need to use Investigation aganst the spell save DC to find it. This answers the questions posed in full.

I don't know what you're coming up with about traces and things for. Why ignore the spell's words and come up with something different to find - why is "being able to find the glyph" not good enough for you?

This is D&D, not Sherlock Holmes, after all.