As long as you ain't counting butterflies you will see that threat. When they see you see them, they will change their mind 99% of the time, gun hiden or not.
The best way I've seen this put is "the more confident you are/present yourself to be, the less likely you are to be a victim, because the criminals won't see a victim."
In a perfect world of "honest" criminals, yes this would happen. Every crime isn't a surprise attack, and some criminals are very brazen.
If you check out some interviews with criminals in prison, 99% of them say the same thing: if they know, or even suspect, that someone is armed, they will move on to the next person. Same is true of burglars when it comes to alarm systems and dogs.
Most criminals look for the easy target and bypass the hard ones.
If you appear confident, they'll walk on by. I always, armed or not, make sure that I present myself as an imposing, confident figure; I've been told that I'm intimidating. I always found that kind of amusing, since I'm only 5'8". I'm 99% certain that I've prevented attacks simply because of how I carry myself. I've seen them coming, seen it in their eyes, and had them walk on by.
I had two guys standing behind me in the men's room of a convenience store, literally talking about jumping me (they were whispering, but not quietly enough) and once one of them realized I knew they were there and what they were planning, they walked away. All from a change in my stance as I was...finishing up. I'm glad they left, because I was standing there trying to figure out how I was going to survive it.

I did appreciate that they seemed to intend on waiting until I'd zipped up.
There are a small percentage that just don't care and are going to do what they are going to do. I would put this heavily on gang bangers who are more concerned with "respect" than they are with life. The kind that will kill you for looking at them funny. But these aren't people that are looking to rob you; they're coming after you for some perceived slight or because of some need to kill.
Now, when it comes to drug addicts, whether strung out and needing money for their next fix, or already high, you're talking about a different beast entirely. Those who are strung out are oblivious to the danger and may be desperate enough that even if they see it, they won't care. Or they will care and run away screaming.
Those who are already high aren't going to see it and don't care. Some of them may even see it has more of a challenge, depending on what they're on. Of course, this is a smaller percentage, because most highs make them chill out/have fun, not go looking for trouble.
You can pretty well count someone who is high and looking for trouble, or a gang banger, as a "determined" threat who is not going to stop unless they're dead. They don't care if it's jail or the grave.
Drug addicts who are strung out, while obviously still a threat are, generally less determined than those above and more likely to bolt from a brandished gun or to stop an attack before they're dead. They want money and to live. For them it's about the high.