Gypsy man features in Post Office advertisement (5)
I believe the answer is:
promo
'advertisement' is the definition.
(short for promotion)
'gypsy man features in post office' is the wordplay.
'gypsy man' becomes 'rom' (I've seen this before).
'features in' is an insertion indicator.
'post office' becomes 'po' (abbreviation).
'rom' inserted inside 'po' is 'PROMO'.
(Other definitions for promo that I've seen before include "Ad" , "Publicity for project or product (abbr)" , "Advertising film or video" , "Encouragement" , "advertisement" .)