I always use my good old 1D mark ii (my daughters have nicknamed it "la Bête" because of it's size and the roar it emits when it takes pictures).
It's big and loud, incredibly fast with it's 8,5 pictures per second, witch make it even more audible.
I'm also not particularly small myself, and I seldom go unnoticed, for some unknown reason.
Even with all this, people don't seem to mind me taking photographs, they just go about their business. When I'm uncertain, I simply talk to them and everything becomes fine almost always.