The earliest lapel pins were made as adornment, rather than statements and are difficult to distinguish from pins or brooches. Lapel pins, however, are typically smaller in size than decorative pins and brooches, usually measuring no higher than one inch.
During the American Civil War, lapel pins were introduced to the armed forces. They were worn by a soldier to distinguish which unit he was fighting in, and to encourage a sense of loyalty and camaraderie within the unit.
But by World War I, the significance of¬†the lapel pin had changed. Instead of being given to all soldiers as a way to differentiate units, lapel pins were awarded to select individuals to distinguish them for exemplary service in the field. Using lapel pins as an award for service¬†is still a common practice¬†in all branches of the armed forces today.
Inspired by their military use, politicians and patriotic citizens started wearing pins to show support for their country. Wearing patriotic lapel pins is a global tradition that extends from the United States to China to Russia.
Later, other groups began using lapel pins. Civic organizations, religious groups, fraternities and sororities, for example, often wear membership pins to their meetings and events. Lapel pins are also used by schools, sports teams, charities, and businesses to promote loyalty and rapport. Colored ribbon lapel pins are also a popular way to raise awareness for causes like breast cancer, child abuse and domestic violence.
For more on the history of lapel pins, read this article from ehow.com .