Brewer's: Good Wine needs no Bush
It was customary to hang out ivy, boughs of trees, flowers, etc., at public houses to notify to travellers that “good cheer” might be had within.
Some ale-houses upon the road I saw, And some with bushes showing they wine did draw.
Poor Robin's Perambulations (1678).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894