。
No entry except for those with business.
Literal
Business except [topic-は] entry honorific-refusal.
A terse public-sign register. 用事 ('business / errand'), 以外 ('except / other than'), 入場 ('entry / admission'). お断り ('refusal / decline,' with the honorific お prefix) is a set phrase for 'not permitted.' Compact signage style.