Ridiculous sign carried by daft poseur (12)
I believe the answer is:
'ridiculous' is the definition.
(I know that absurd can be written as preposterous)
'sign carried by daft poseur' is the wordplay.
'sign' becomes 'poster' (poster is a kind of sign).
'carried by' means one lot of letters goes inside another.
'daft' indicates anagramming the letters.
'poseur' is an anagram of 'preous'.
'poster' placed within 'preous' is 'PREPOSTEROUS'.
(Other definitions for preposterous that I've seen before include "Ludicrous" , "Quite absurd" , "Utterly absurd" , "Laughable" , "Crazy" .)