C.R.S. § 34-21-109: Code of signals.

There shall be established by the commissioner a uniform code of signals, embracing those most generally in use in metalliferous mines, which shall be adopted in all mines using hoisting machinery. The code of signals shall be securely posted, in clear and legible form, in the engine room, at the collar of the shaft, and at each level or station. In all shafts equipped with cages, such shafts and cages shall be fully equipped with a system of electric signals from such cages and stations to the engineer wherever possible.