Notice a lady is president twice (5)
I believe the answer is:
adams
'president twice' is the definition.
(US presidents John Adams and John Quincy Adams)
'notice a lady' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'lady' becomes 'Ms' (alternative to Miss or Mrs).
'ad'+'a'+'ms'='ADAMS'
'is' acts as a link.
(Other definitions for adams that I've seen before include "John Quincy --, sixth US president" , "Second and sixth US president" , "Richard --, Watership Down author" , "Ansel --, US landscape photographer" , "Sort of apple" .)