Flyin-Low is pretty close.

1. Not a commemorative, and not a issued carry piece. Sold to ISP employees only in November 1974 for $150.

2. The number in addition to the serial number was the PE (personal employee) number of the unit purchasing it. S&W would only inscribe 3 numbers. Most units had a PE number in the 4 digit range but S&W only printed the first 3. ISP PE numbers are only used once and can be used to estimate length of service. My guess is this unit's PE number was 254? which would make his hire date somewhere in mid-1970s. Badge numbers were never used on these guns.
3. The first true "commemorative" was the M66 6" with presentation box in 1983. These were followed by a Ruger .223 stainless rifle, a Glock, a Baretta, and a some kind of knife. There were no numbers other than the serial on these guns. I've never seen any numbers on the box that did not pertain to the gun, maybe some kind of inventory number, but I don't think it was added by the ISP.

Many guys thought these guns would become collectors items at sky high prices. This did not happen. Presently both of these S&Ws can be purchased for about the same as the same model without the bells and whistles.

Let's just say I was there.