Most times with a larger camera I carry it with a hand over the top of it to disguise its size or shift it to the side of my body, and for TLR's only open up the viewfinder hood when I am about to shoot.

Though on two occasions this past week I have heard people exclaim about the cameras I was carrying. First a fruit stand owner and his older friend/father requested their pictures to be taken with my Seagull TLR, and yesterday while walking around with the big ol texas leica (fuji 690ii) two men walked by, and one grabbed the other's arm and pointed to my camera saying "look at the size of that!"