This coin dates between 1903 and 1919. I think the last digit was intentionally removed, but that doesn't make it any less interesting.
The holes are too large for rivets or nails suggesting it was probably drilled to be worn. With that in mind, here's a possible long shot scenerio:
When googling the 191rst, the only outfit that comes up is the 191rst engineers. There is almost nothing about them that I can find so far except this:
"Here's a photo from the book (pardon my scan) of Capt. Clinton S. Brown, stepson of General George C. Marshall as he sails off with the 191rst Engineers."
*Marshall's name is significant here, as he served in the Phillipines 1902-03 and 1913-16, one of who's dates is probably when the 191rst sailed.
Research gets fuzzy now, as the only stepson of General Marshall mentioned in his biographies is Tupper Brown (who was killed in WW2).
It seems that the author who described the photograph was wrong in its attribution, but may not have been wrong in describing both General Marshal and the 191rst sailing together.
Anyway, if I were to take a wild guess, I'd say that this coin was worn as a makeshift i.d. by a member of the 191rst engineers sometimes between 1903 and 1916, while serving in the Phillipines Islands.