Kind of true. The hammer and sickle as a combined symbol was a creation of the Soviet period. The hammer represents the proletariat, wage laborers. The sickle represents the peasantry.
In orthodox Marxism (as opposed to Marxism-Leninism), the peasantry are seen as not having significant revolutionary potential, and it is the movement from peasant societies to industrial societies which creates the necessary working class for a revolutionary transition to socialism. But there was no widely adopted symbol like the Soviet hammer and sickle - a variety of diverse symbols (including hammers and sickles separately) were used by socialist groups before the Soviet Union.