。
Good wine needs no sign.
Literal
Good-wine [topic-は] sign [object-を] does-not-need [classical-ず].
A classical proverb. 良酒 ('good sake, good wine'). 看板 ('signboard, shop sign') — a reference to signboards advertising taverns. 要せず uses the classical negative ~ず (equivalent to modern ~ない). A concise observation about quality speaking for itself.