。
Please come again.
Literal
Again honorific-come [please-ください].
お越し is the honorific nominalization of 越す 'to come over,' part of the respectful (sonkeigo) pattern お+[verb stem]+ください — a polite request for the listener to perform an action. This exact phrase is the stock farewell used by shopkeepers, innkeepers, and hosts after a visit; compare いらっしゃいませ used on arrival.