It wasn't completely a given, though -- signs were there to tell a peasant what that business did, for example, since a lot of them couldn't read.
For a blacksmith, it was an anvil; for pawnbrokers, scales.
Incidentally, that's where surnames came from; Hooper if you made barrels, Smith if you were a blacksmith, Butcher if... well, you know. If you had multiple "Daves" in a village, calling someone "Dave the Butcher" eventually became "Dave Butcher", to differentiate from "Dave", "Dave," and "Dave".
But yeah, literacy in things like (to us) old German, French, Norman, Norse, and English (or their predecessor languages) was a lot higher than what people, and the media, believe.