What would the police be able to do though for someone just staring? I can't imagine them saying "Louise Rogers, I am arresting you under suspicion of staring at Thomas Adams". I'd be worried about being charged myself for wasting police time.
Could a court of law rule staring as harrassment? I also think it's important to note that people with brown/black eyes can be difficult to determine where they are looking as their pupils are not always visible. For example a man could be looking out of the window at the Somerset countryside on his train trip and someone may mistakenly think he is looking at them.
Nobody wants to see people being groped and sexually assaulted but when it comes to a poster that is marked Police then I personally feel they should only be following up legally enforceable offences.
I find your comments interesting
@LowLevel , that you interpret staring as a form of aggression. I guess we all react differently to certain behaviours. Would you speak up if someone was staring at you on the railway? Would you tell the Guard?