Notice Nick appearing in ... (6)
I believe the answer is:
caveat
'notice' is the definition.
(I know that caveat is a type of notice)
'nick appearing in' is the wordplay.
'nick' becomes 'Cave' (Nick Cave is a musician).
'appearing in' becomes 'at' (eg appearing at or in a theatre).
'cave'+'at'='CAVEAT'
(Other definitions for caveat that I've seen before include "Vacate (anag) - warning" , "A notice or warning" , "'Warning, proviso (6)'" , "Cautionary warning" , "Let the buyer beware ...emptor" .)