You'd be surprised at what your wallet can say. Several years ago I ate at a Taco Cabana in East Houston with a 30.06 sign. I emailed C.S. and said my family and friends would not eat at this place again as long as it was posted. The response surprised me; it was NOT company policy to restrict legal carry! Some time later, we ate there again to notice that the sign was gone, and in its place was the generic TABC 'unlicensed carry' sign. Horray for our side! It was an easy victory, it's not like I, with the power of myself, changed Taco Cabana corporate policy, I just pointed out a chain store that did not follow it. But I'll take it.
I get a chuckle when I walk into the big-box-stores/corporate dwellings that have gunbuster signs. These companies no doubt have massive, massive legal teams working for them, and such a law change as the 30.06 posting shouldn't get past them. I almost think that they are, in fact, on our side. Think about it, at anytime they could post a 30.06 sign on a whim, but they don't; they leave it at "no weapons" or "no handguns" allowed. I really interpret it as the company enforcing private property laws that we (as customers) are not 'in control' of that private property and thus are not authorized to open carry handguns, long guns, bowie knives, etc. It's almost as good as "CHLs welcome" signs. That's my unwarranted two cents. And worth every penny.
And I'm one of those nit-pickers...

I would just love to get in an argument with this kind of guy (the teller in the OP's story) and show him the error of his ways. But that wouldn't be very conducive to furthering our effort. Like others have commented, this conversation would not have happened to me, if it's not legal, I don't even bring it up. If the company wants to post some kind of sign like that, it's their responsibility to research the legality of such notice, and I'm not going to educate them in such an endeavor.
If that is one of your 'no-nos' for purchasing the services of an establishment, however, I highly encourage you to talk to management and vote with your wallet. And more power to you!