Um... it's not illegal to take a photo in a bank. The most they could do is simply ask you to stop. No harm done. It's easier to ask for forgiveness than permission.
Um... READ my post #7, where I said, while it may not be outright illegal to take photos in a bank... I will add now, that a private institution could enforce or misconstrue what someone is doing using a camera in or around a bank in any number of ways. It's simply easier not to use a camera in a bank and avoid being in such a situation were some security guard or nervous bank employee to view one's behavior as suspicious, make a scene or take enforcement actions like taking your camera from you, calling police, etc. And as I stated, I added this note for the consideration of other readers as well as the OP to think about such actions before assuming its safe to do it.
I didn't say that you thought it was illegal. All I'm saying is, if you're not breaking a law, what's the problem? You're not doing anything wrong until somebody asks you to put the camera away. At that point, you're being disrespectful if you continue and they have the right to ask you to leave. Anybody can photograph anything they want to, even inside a bank. Bank employees or security guards can ask you to stop, and then you stop. If they make a scene doing so, it's their fault and they're out of line. And if police are called, that's just about the biggest waste of their time.
"Um..." implied I suggested illegality in the action. Like I said, it cannot easily be assumed how the situation could unfold if someone thinks you are suspicious for using a camera in or around a bank and some people get very upset about being escorted out or made the center of attention when they think they are not in the wrong. While it may be a waste of time, if you are aware of the situation that such things could occur, why even go there when it makes you complicit in the potential to have your actions misconstrued. Asking for permission to photograph is one thing but assuming and just taking photos of anything because you think you can is not how this works, especially inside of a private company. People like their privacy and so do some companies who would prefer to control who is doing what with photography in and around their operations. Mutual respect by asking permission and only taking photos when that is granted is the way to go.
I didn't mean to imply that with the "um." I understand what you're saying. Yes, it may seem silly to knowingly put yourself in a situation where others might hassle you. And I've personally never had any interest in taking photos in, of, or around a bank. But I enjoy having the right to behave how I want to, so long as it's within the confines of the law. If I had an interest in taking photos inside banks, I'd be doing it until I was told to stop. I wouldn't care if people gave me funny looks or whatnot. I'd stop if they said so, otherwise I'd just be acting like a jerk. Sometimes new tellers give me funny looks if I'm back for the 2nd or 3rd time in a week dumping a $500 bag of half dollars. If they ask, I tell them about my hobby. If they don't, I don't worry about what they're thinking, or if they're suspicious, or not. Again, I understand you're saying that it seems silly to put yourself in an odd situation. My counterpoint is just that people have the right to put themselves in that situation if they choose to do so.