click on this link to see full picture, symbol is in top r/h corner of grave marker
The left corner is a Mason symbol, so perhaps the right is related.
Cropping to upload.
Full size on click.
There were "brotherhoods" of Masonic railroad workers, so that would fit with the Masonic "G" on the outer rim and the "R" in the center.
Melanie, I tried to add some color to show you what I'm seeing in these intertwined letters. Not saying I'm right, necessarily, just that this is what I see... But after reading what C-H wrote about the railroad connection, I wonder if it could be the logo for a railroad. I don't think it's the logo for the Chicago, Burlington, and Quincy (I just looked that up), but perhaps it is the logo for something else connected with the railroad, like "Conductors of Railroad" or some such (which would account for you seeing the "C" and me seeing the "R.") You're right, nothing about this emblem is as clear as what is elsewhere on the stone.
See this...Order of Railway Conductors, for example.
...or This....Vintage Pin
I could see it being ORC, but cannot find that as a logo.
ETA -- that pin, now, that could be what it is.