A sign car vacated garage earlier on (6)
I believe the answer is:
gemini
'a sign' is the definition.
(Gemini is a star sign)
'car vacated garage earlier on' is the wordplay.
'car' becomes 'mini' (Mini Cooper).
'vacated' suggests removing the centre (internal letters vacate the word).
'earlier on' is a charade indicator (letters next to each other).
'garage' with its centre taken out is 'ge'.
'mini' put after 'ge' is 'GEMINI'.
(Other definitions for gemini that I've seen before include "set of twinklers" , "Castor and Pollux constellation" , "Twins constellation" , "Third zodiacal sign" , "lot of stars" .)