Poster endorses rising car brand (5)
I believe the answer is:
skoda
'car brand' is the definition.
'skoda' can be an answer for 'brand' (I have seen 'Brand of car ' mean 'skoda' so perhaps 'brand' could also mean 'skoda'). I'm not certain of the 'car' bit.
'poster endorses rising' is the wordplay.
'poster' becomes 'ad' (short for advert).
'endorses' becomes 'oks' (I've seen this in another clue).
'rising' says the letters should be written backwards (letters written upwards in a down clue).
'ad'+'oks'='adoks'
'adoks' back-to-front is 'SKODA'.
Can you help me to learn more?
(Another definition for skoda that I've seen is " Brand of car".)