This question was asked a while ago and got quite a few upvotes, but never got answered: https://www.reddit.com/r/AskHistorians/comments/2u6yij/are_the_nail_marks_on_the_walls_of_auschwitz_gas/
I tried looking online but couldn't find anything that seemed reliable and figured this would be my best place to ask aside from a stackexchange site.
From the post:
I can't speak for the entirety of the time Auschwitz has been opened to tourists, but from my own experience, the rules concerning entering the gas chamber ( complete silence, no cameras, no touching) are heavily enforced, so it might be possible for them to have been made by tourists, but unlikely.