I've paied attention to those around me during the few times I'm OC'ing, I can't help it actually. It's obvious some see/notice my sidearm but, for the most part, the people just keep on going about thier business. Some may see it but ignore it/don't care, but there a bunch in their own safe little universe who go about their 'bidness' blissfully unaware of anything too.
I've gotten a few questions from those enquiring minds who just have to ask.
Your right though, body language, demeanor.........people who actually see a sidearm open carried will asses the threat by what they see most of the time from the carrier.