Cart ignoring first symbol on road sign (5)
I believe the answer is:
arrow
'symbol on road sign' is the definition.
'cart ignoring first' is the wordplay.
'cart' becomes 'barrow' (barrow is a kind of cart).
'ignoring first' means to remove the first letter.
'barrow' with its first letter taken off is 'ARROW'.
(Other definitions for arrow that I've seen before include "Missile with a point" , "Quarrel, fired from crossbow" , "Slender, pointed missile" , "The bowman's missile" , "One in a quiver" .)