DoubleActionCHL
Well-Known
I don't know about LEO being able to spot. As far as I know, they're trained to spot criminals carrying, and the average thug isn't a big fan of using a holster. There are a bunch of tells, mainly that the guy's hand keeps going back to the gun to make sure it stays in place.
True, but they're also aware of the style of dress one must adopt to carry concealed. For instance, a man with a t-shirt and an open button up over it is more likely to be carrying than a guy with only a t-shirt.
This isn't really limited to law enforcement. Anyone with a little knowledge of concealed carry methods and look at a group of people and pick out the ones who are likely carrying... except for the women, of course.