They call them the " Battle of Britain" Colts.
The BritishGov't took every .38 cal and .45 cal handgun they could get.
Check to see if the cylinder has been rechambered to .38 S&W - most of the .38 Special/.357 Magnums had a .38S&W reamer run into the chambers.
To me it looks like the finish has been chemically stripped - leads me to think someone may have removed or tried to hide the .38-200 proof marks.