"For sale by" sign poster (5)
I believe the answer is:
owner
'for sale by sign poster' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for owner that I've seen before include "Person having property" , "One who has something" , "Person with legal title to something" , "Holder, proprietor" , "Legal possessor" .)