I suspect they really are oblivious to it. Either that or they don't have the nerve to ask you about it. In the time I've been OCing I've gotten a few "Are you a cop?"s, one "Why do you need a gun, man?", one "Is that a Springfield?" (I carry a USP .45 fullsize), and one "Every time I see you in here I'm glad, because I know you have it for a good cause" from the security guard that works at the local Aldi.
This amongst the countless hundreds of thousands that have encountered me while carrying. Your experience sounds entirely typical to me, and welcome to open carrying!