Use the Union Label-May 1 Reminder

One way to stake out union turf—that’s as old as organizing itself —is the use of graphics as union labels. All trade unions developed a logo that identified their trade sector as well as organizational name. The logo of the International Brotherhood of Teamsters, formed in 1903 with the amalgamation of the Team Drivers International Union and the Teamsters National Union, still bears two stylized horses, and the International Association of Machinists display the square and calipers of their trade.

--From Lincoln Cushing LABOR CULTURE.