This is the "Medal for Merits to DOT Volunteer Detachments of Labors" from the Bulgarian Peoples Republic. Instituted in 1954, it was awarded for "bravery, heroism, and self-sacrifice for guarding the peoples order, national borders, and safety of traffic on the roads". the Volunteer Worker Corps or "Otriadniki" were an army of volunteer labor that worked on all kinds of public works projects.