Who was Petar Velev? I found another postcard with a Monument of Petar Velev in Peshtera. As known from the Bulgarian Wikipedia, he was a member of the communist Batak partisan detachment during the partisan movement in Bulgaria (1941 - 1944). Died in 1944.
The postcard is from 1975, Maybe, the cinema opened just before.
There are (or were) plans for a museum of socialist cars in the large hall of the empty cinema.
At all, Bulgarian films are very unknown. I only remeber watching Tilt in 2013, a film about youth in Bulgaria in the early 1990s. I liked it.