See advertisement (6)
I believe the answer is:
notice
I believe this clue is a double definition.
'see' is the first definition.
(notice can mean to see or realise)
'advertisement' is the second definition.
(I've seen this before)
(Other definitions for notice that I've seen before include "Advance warning of an event" , "Notification" , "Instruction" , "This is usually given before quitting job" , "Advance indication of intention to resign" .)