I make it a point not to say anything to someone when I see them attempting to Conceal carry, especially when they fail.
But it's probably not be in their best interest, our ours. Someone not so understanding might be the next to notice, and cause them a lot of grief, and a lot of bad press in general. With a word and a tuck it could all be avoided. If they are intending to CC, I'd think it a curtesy to let them know they aren't.