A recent Supreme Court ruling just gave the police a free pass to stop and bother anyone they think might be engaging in criminal activity, without any justification.  It will now be perfectly legal for the police to pull you over, or stop you on the street, and ask for identification (or any other intrusive questions).  Anything they find can be held against you, after gathering their information. This is particularly true, if it turns out you have an outstanding warrant for something as simple as a traffic violation.