Frank impression (5)
I believe the answer is:
stamp
I believe this is a double definition.
'frank' is the first definition.
(frank can mean to mark with an official stamp)
'impression' is the second definition.
(I know that impression can be written as stamp)
(Other definitions for stamp that I've seen before include "Impress with a mark" , "Philatelist's item" , "Mark of approval" , "Validation for a letter - tread heavily" , "Postage paid label" .)