C.R.S. § 18-12-103
18-12-103. Possession of a defaced firearm
18-12-103. Possession of a defaced firearm. A person commits a class 1 misdemeanor if he knowingly and unlawfully possesses a firearm, the manufacturer's serial number of which, or other distinguishing number or identification mark, has been removed, defaced, altered, or destroyed, except by normal wear and tear.