Well, not exactly "adopted by the Russians" since it was already an international symbol of the struggle in which they were participating. OK, nit picked. :-)
The hammer-and-sickle was conceived in l917, immediately after the workers took power. Legend is that Leon Trotsky himself suggested it. It refers to a very specific event. The Peasants' Councils national organization formally allied with the Workers' Councils national organization to form the new government, and this agreement of town and country guaranteed the success, for the moment, of the revolution. Thus, the workers' hammer, the peasants' sickle.