Lapel pins, Arm Bands etc
Lapel pins and arm bands are a sign saying "I support x group" wearing the pin is a form of commitment to a task. You have already showed support. So once someone shows support they will likely comply with the next task.
Wearing an arm band or lapel pin also gives a sense of having similarity with the rest of the group. Symbols and lapel pins also help with political recruitment. That is why buttons, and lapel pins are given out to those at political meetings. The most infamous use of arm bands are the Nazi party and later the war protesters. Because of that buttons and pins are more advisable for your cause. Pins and buttons are best because they can be worn on a suit.