Fimble McGee, Gnome Illusionist
Fimble nods. "Absolutely." Fimble walks over to the left side of the right tunnel. He looks for a dry spot and in gnomish he scrawls a number 1 in white chalk. "I'll put them on the left side of the tunnel, so if we come out of a tunnel we've already went through, we'll see the chalk number a little bit easier. I'll just keep my eyes on the right wall."
OOC: Not sure if gnomish has seperate numerals than other languages. Fimble knows Common, Gnome, Draconic, Elven, Goblin, so whichever has the most uncommon numerals will be what he is writing in.