I carried one of these when I worked for the Post Office Railway Mail Service back in the 60's. I picked this up about 10 years ago when browsing a small gun shop. I don't believe the owner knew what it was as he called it a short barrel Police Positive.
I knew exactly what it was as I carried one back in the day
...a working man's gun and it shows. It dates to 1930 and locks up tight as a drum. After a little dickering I walked out the door with this package...gun, holster and ammo all period correct for $ 200. I've put a few rounds through it. Brings back some great memories working on the mail trains.
Here's a few pics. Rich
COLT BANKERS SPECIAL R.M.S