This is an interesting recurring thread...it will come back again. In the USA with a few exceptions we can shoot anything we can see in or from a public place. Some public places may restrict tripods (for safety reasons) or photos of art works or use of flash (to protect art or prevent distractions) but but most of the time you can shoot what or who you want from a public place. That, however doesn't mean you can publish what you shoot in a public place. If you shoot a private property or person and publish the shot without proper permissions, you may be civily liable (as distinguised from criminally liable). I can shoot your house from a public place but the person who places the image in a magazine, newspaper, pamphlet, etc may have liability. The rules are complex and ensure lawyer full-employment. So, if I shoot your house and put the picture in the newspaper, especially in an advertisement I could be liable...however, if you are murdered in your house and I photograph it as a photojournalist covering a crime scene, the image can be published in lot of places without liability.
There's a high end town in Florida where I'm told it's illegal to take pictures or to even carry a camera in public...the story I was told is that the town is full of wealthy celebrity types and they don't want "tourists" taking pictures. I don't know if this story is true but I suspect that if it is true and you were arrested you might have it overturned as unconstitutional in the Supreme Court.....if you had enough money to get that far. The problem is you would be trying to out-spend millionaires. Not worth testing the law at my fiscal level.
If you are photographing public transit facilities or potential terrorist targets and a police officer sees your actions as suspicious (for reasons he/she can reasonably articulate in court) he/she may talk to you to find out what you are doing. This is a reasonable course of action in this day and age. Some officers may go beyond their authority in these circumstances but good judgement and a good attitude will go a long way to keep the situation mellow....and that applies to the police officer as well. If the officer is out of line, you can always call the police department and ask to speak to a supervisor. In fact, if the officer is clearly wrong and unnecessarily heavy handed, get the name, badge number date and time, names of witnesses, and make an official complaint with the Department...not the officer. If you start out heavy handed with an officer's reasonable inquiry, don't expect the tone of the contact to get better. I've never been stopped while taking photographs in public and I was in law enforcement for 34 years and never had occasion to confront a photographer....but that was before the modern era of terrorism.
Chuck