Carry motorway sign (5)
I believe the answer is:
totem
'sign' is the definition.
(I've seen this before)
'carry motorway' is the wordplay.
'carry' becomes 'tote' (toting is a kind of carrying).
'motorway' becomes 'M' (as in motorway names - Mt, Me etc).
'tote'+'m'='TOTEM'
(Other definitions for totem that I've seen before include "Symbolic pole" , "Native American symbol" , "Pole used in ritual" , "Animal as clan symbol" , "Symbol given (undue) respect" .)