Different states have different rules. In June the U.S. Supreme Court struck down Minnesota's prohibition on wearing "political" buttons, clothing, or other insignia at polling places. While the court noted there is room for some prohibitions, states are trying to avoid getting sued for violating first amendment rights until the parameters are more precise. Prior law clearly allowed a 100-foot radius, but now the scope of what can and cannot be prohibited in that radius is up in the air.