I was thinking about it the other day walking through the parking lot at work. I haven't seen a single one of those stickers, license plates, or any similar "TBL" reference since I've been in AZ. The two big cop shops in the Springfield area back in MA (Guardian and Sentry) sold them, but the cop shops here in Yuma don't have anything like that in stock.
I was talking to a friend yesterday that retired from the Mass State Police years ago about this and his comment was that they started having them get licensed for when they were off duty. He said they were issued 2 guns the second I believe he said was a S&W Model 60 and they were supposed to have that with them when off duty and have with them at all times. He didn't like that part if he wanted to go out drinking.
A late friend of mine told me about two different federal agents he knew (one ICE, one FBI). Both told similar stories that happened when they got stopped for a traffic violation by MSP while off duty. When they handed the trooper their federal badge and creds, the trooper told them that it was illegal for them to carry off duty without an LTC and wanted to disarm them. After an extended time on the side of the highway, the trooper let them go without confiscating their federally issued handgun.
I can only think of three possible explanations: 1) stupidity, 2) testosterone poisoning (aka, my badge is better than your badge), or 3) both.