I will notice them returning about decoration (9)
I believe the answer is:
medallion
'decoration' is the definition.
(synonyms)
'i will notice them returning about' is the wordplay.
'i will' becomes 'I'll' (abbreviation).
'notice' becomes 'ad' (both can mean an advertisement).
'them' becomes 'em' ('em is an informal way of saying 'them').
'returning' is a reversal indicator.
'about' becomes 'on' (as in a book 'on' a certain topic).
'ill'+'ad'+'em'='illadem'
'illadem' written backwards gives 'medalli'.
'medalli'+'on'='MEDALLION'
(Other definitions for medallion that I've seen before include "Mad O'Neill wins the award" , "Cut" , "(Commemorative) disc" , "Round pendant" , "Large coin-shaped metal ornament" .)