It should be made a felony for any law enforcement officer to fail to display a badge, or otherwise obstruct their badge number while on duty at public events, protests, marches, or other large public gathering.
The practice in law enforcement of hiding or covering up of the badge number is an attempt to remain anonymous while taking part in potentially illegal activities, and should thus be seen as conspiracy to commit an illegal act, and potential abuse of authority.
Because law enforcement officers should be seen as role models, and who's job is to uphold the law, this obvious attempt to hide illegal action should have severe consequences.