So I want to make a shifter character and if my character finds a shadow tattoo how would it work wen my character changed into a different person would the tattoo still be on my character and also the aberrant dragonmark I would appreciate any help thanks 

Nothing about the Shifter race changes you into a different person. The racial feature isn't a polymorph, so all tattoos will remain in place.

Ok thanks I misunderstood the shifter race I thought you would change in a different person tanks for letting me know I appreciate it 

If you are looking to change into a different person, check out the changeling species. 
And still, I’d think magical tattoos and aberrant dragon marks would remain in place no matter who you look like. 

I’d regard the tattoo as equipment. If it’s the Changeling you’re thinking of (who change appearance much more completely than the Shifter does), then their equipment and clothing does not change when they do, so the tattoo will remain visible and functional. (I don’t know about the dragon marks.)

[As a house rule, if the player wanted the tattoo to disappear when they change appearance, then I’d probably rule that they don’t benefit from its effects.]

Ok thanks for all the information I appreciate it and yes I was thinking of the changeling species.