http://law-faq.com/13/dealing-with-police/can-a-police-officer-stop-you-for-no-reason/
Can a police officer stop you for no reason?
Posted by Nauseum on
August 29th, 2011
There may be a reason even if they didn’t tell you.
The burden of proof to stop someone is called “reasonable suspicion”. The burden of proof to search someone is called “probable cause”.
When it appears that you have been stopped for no reason it is called a “Terry Stop”. The name comes from the standards established in a 1968 case, Terry v. Ohio. Remember, all the police need at this point is a ‘reasonable suspicion.’ Police will use a Terry Stop as a tool if he or she observes unusual conduct which leads him or her to reasonably suspect that criminal activity may be occurring. This is a gray area and left to interpretation.