A portable advertising placard (8,5)
I believe the answer is:
sandwich board
'a portable advertising placard' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sandwich board that I've seen before include "I come along road with the bill" , "Advertising hoarding carried up and down a street" , "Ad-carrier strapped on" , "Moving advertisement" , "Advertisement carried on the person" .)