I'm of the opinion that I wouldn't want anybody to know I was carrying unless I was actually intending to shoot. If I had to reach for a pistol, then I would shoot, because by the point I reach for it I would have exhausted all other reasonable options, such as trying to talk them down or flee.
Waving a gun around, or even suggesting you have one is not a reasonable option in my book. Sure, some people might be scared off by it, but others would see it as even more reason to attack you. After all, they get a new pistol out of the deal, and in thier mind if you had the sack to shoot them, you wouldn't bother threatening them.