E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Sharps the word. Look out, keep your eyes open and your wits about you. When a shopman suspects a customer, he will ask aloud of a brother-shopman if Mr. Sharp is come in; and if his suspicion is confirmed, will receive for answer, No, but he is expected back immediately. (Hotten.)