Sign for car by empty garage (6)
I believe the answer is:
gemini
'sign' is the definition.
(Gemini is an example)
'car by empty garage' is the wordplay.
'car' becomes 'mini' (Mini Cooper**).
'by' means one lot of letters go next to another.
'empty' suggests removing the centre.
'garage' with its middle removed is 'ge'.
'mini' put after 'ge' is 'GEMINI'.
'for' is the link.
(Other definitions for gemini that I've seen before include "Third zodiacal sign" , "set of twinklers" , "Zodiacal twins" , "Twins constellation" , "Zodiac sign - the Twins" .)