I'm going to linger a bit longer in 1948 Bulgaria with some more favourite communist themes on its stamps. Sport is one of those, it being used as a good way to profile the country and to profile "the good cause".
And solidarity, too, may be a way to show the world that communist countries stick together like a proper bloc.
This stamp is from a set issued to honour the friendship pact between Bulgaria and Rumania (or is it Romania? I'm never sure, but Google seems to prefer the latter by a large majority) and features the proposed bridge over the river Danube (the "friendship bridge" was eventually built in 1954) and the flags of the two countries.
But I suppose on top of the list is the "worker" theme. Many definitives and commemoratives of this era glorify the hard-working labourer, such as this stamp issued on the Day of the Miner.
Even when something as decadent as culture (eg classical music) is portrayed, a communist twist is given to the design, with workers as the audience.
It's fascinating stuff, really, if you take the time to study them a bit more closely!