I shoot in a lot of areas where I can't look like I have a camera so that I don't get robbed. I either get a camera bag that fits my my backpack or take a trip down to the camera store for some old vintage bag of some sort, strip off any tags or logos and it doesn't look much like a camera bag. Or as David suggested the Think Tanks don't really look like camera bags at all, but they do look like you might have something expensive such as a laptop in them. Also, they look pretty modern and somewhat expensive, which is pretty heatscore in itself, depending on the purpose.