Bonkers sign mostly about wine (7)
I believe the answer is:
madeira
'wine' is the definition.
(Madeira is an example)
'bonkers sign mostly about' is the wordplay.
'bonkers' becomes 'mad' (I've seen this in another clue).
'sign' becomes 'Aries' (star sign).
'mostly' means to remove the last letter.
'about' shows that the letters should be reversed in order.
'aries' with its final letter removed is 'arie'.
'arie' backwards is 'eira'.
'mad'+'eira'='MADEIRA'
(Other definitions for madeira that I've seen before include "Fortified wine from Atlantic island" , "cake producer" , "Atlantic island, famed for its sweet wine" , "Portuguese North Atlantic island" , "A fortified wine, a rich sponge" .)