Captain America's shield is used as a defensive equipment.
Law enforcement shields often have a large signs stating "POLICE" (or the name of a force, such as "US MARSHALS") to indicate that the user is a law enforcement officer
 Finally, shields vary greatly in shape, ranging in roundness to angularity, proportional length and width, symmetry and edge pattern; different shapes provide more optimal protection for infantry or cavalry, enhance portability, provide secondary uses such as ship protection or as a weapon and so on

