If the city asks you to leave, having an email isn't going to negate that. If they ask you to leave, and you refuse because you think you can just wave your permission slip, they'll just have the police remove you, and let a judge decide. It's better if nobody knows you're there, or have been. Someone complaining is not going to look at your email either if they have it in mind that you're doing something wrong. Knowing what the rules are is all you're really after, and that can be found by looking them up yourself. Asking someone for permission, presumes to them that for some reason you NEED permission, or why would you be asking. That gives them the power to decide. Well, guess what the usual answer is? Yes, and they put their butt on the line. No, and they're safe from criticism from superiors. What do you think the majority of them will say?