Here are a couple pictures of the frame and barrel markings.Nice Colt. Whatever the reason for the marks, it does add to the character, and mystique of the gun and also thoughts of who might have owned it at that time.
Your serial number is the closest to my Colt (150234) that I have ever found. The serial number font on mine is close to yours but not identical. Mine is a 4 3/4" .45 Colt and Letters to H&D Folsom in New Orleans in 1893.
Thanks for sharing the photos. It adds a little to the puzzle of my gun.
Would you care to post a few other photos of yours especially the other barrel and frame stampings? Thanks.