I found this in an article from the Las Vegas Review-Journal:

If someone is around to let you inside the old Nye County courthouse in Belmont, you can look for it on a door frame on the first floor — a simple patch of graffiti that now carries haunting undertones.

Many old-timers in central Nevada believe the mark was left by a member of the doomsday cult, maybe even Charlie himself. And though state officials and historians won’t confirm the notion, they don’t exactly reject it either.