I found a penny the other day and it is a copper 1973 penny with a box carved into it with the initials CO inside the box. Have you ever seen one of these?
Hello, Sean --
A private company stamped thousands of 1970s and early 1980s Lincoln cents with state outlines as a collector series. Yours, a Colorado piece, is considered a novelty coin and worth 10 to 20 cents to those who collect such pieces.