Illrigger - Baleful Interdict:Seals vs invisibilty

Would a creature that turns invisible after a seal is placed on it be still visible to the illrigger (not other chars) or at least the seal placed on it?

The spell states: Once on your turn, you can place a magical seal on a creature within 30 ft. of you. You can either place this seal when you hit that target with a weapon attack (no action required), or you can use a bonus action to place this seal on a target you can see within range. The seal lasts for 1 minute or until burned. Seals are invisible to other creatures but appear to you as glowing glyphs on the creature's body. 

Seems to me that the seal would continue to appear to you as a glowing glyph on the creature's body even if that creature has the Invisible condition.

That condition has this to say about the additional things which become invisible along with the creature itself:

"Any equipment you are wearing or carrying is also concealed."

I would rule that such a magical seal is NOT considered to be "equipment" for the purposes of this rule interaction.

However, the subsequent ruling for whether or not you can actually see that creature for the purposes of spell targeting or having to attack it with disadvantage and so on becomes a bit more complicated and might go either way.  You would certainly know the creature's location, so it wouldn't be "hidden" (at least I would rule it that way), but it might still be "Unseen".

I would say no. The Invisibility spell makes the creature invisible. The ability would need to say that the creature cannot benefit from the Invisible condition against you.