Do they prohibit pennants? (7)
I believe the answer is:
banners
'pennants?' is the definition.
(I've seen this in another clue)
'do they prohibit' is the wordplay.
I cannot quite see how this works, but
'prohibit' could be 'ban' (banning is a kind of prohibiting) and 'ban' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for banners that I've seen before include "Long strips with messages hung in public places" , "Newspaper headlines or flags" .)