VERY old poster - i think?!

i found this in one of the frames i recently purchased. there was a picture on top of this in a very old, plain wooden frame behind a very old and warped pane of glass. the picture in front had been completely ruined by the elements and i through it out. this was behind it though and it looks quite old - and like it has been used. see the holes in the corner where it was probably tacked up? is it worth anything? anyone know how old? would it be worth having it restored? can water marks like these be removed safely?

thanks!