Found this signature in Peterson's Meadow Cave in Montana. There are a lot of 1800's graffiti from the local miners of Anaconda but only this one between 1921 and 2001 that I could find. Thought it was historically interesting, only two years after the start of the NSS.
It reads:
Explored & Mapped
Dec 19 1943
H & B Seidemann
W Nelson
Nat Speleological Soc.