Why do they call a union label a bug?

A union label is often referred to as a "bug" because of its resemblance to a small, often circular design or emblem that can be printed or sewn onto products. The term "bug" is derived from older printing terminology where it referred to a small mark or symbol used to indicate quality or authenticity. In the context of labor unions, a union label signifies that a product was made under fair labor practices, and its presence serves as a badge of pride for union workers.