I think that’s a bit of a mistake to concentrate on spotting concealed handguns. Like as not, the person carrying is doing so legitimately.
I’ve read that the numero uno survival skill among LEO’s is to know how to spot guys who’ve done time in prison. Armed or not, THEY’re to ones you need to watch out for.
FYI
Except in Bloomberg's NYC where the odds are 1 in 10,000 that the person packing is legal.
I started being a lot more observant after I was walking to my car in a shopping center lot one day, and was accosted by a clearly deranged man. All I could think of was getting my door unlocked as quickly as possible. I wasn't fast enough to avoid having a large drink of some sort thrown in my face, and all I could think was, "Thank you God, that was the only weapon at his disposal".