It's a normal imperative.
No, I'm not familiar, but I think there might be something like it in Russia. I don't exactly know the origin of the word "воробей", but the birds are kind of a bad guys - "воробей" sounds very semiliar to "вора бей" or the same "бей вора" (beat the thief). The bird is probably inclined to steal, but, I suppose, you may have known it without me.So my question for Russians is this -- are you familiar with the variant in which воробьи are the "villains" and ласточки are the "good guys"