European scheme to keep motorway sign up (6)
I believe the answer is:
employ
'sign up' is the definition.
(thesaurus)
'european scheme to keep motorway' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'scheme' becomes 'ploy' (I have seen 'Tactical scheme' mean 'ploy' so perhaps 'scheme' could also mean 'ploy').
'to keep' is an insertion indicator.
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'e'+'ploy'='eploy'
'eploy' placed around 'm' is 'EMPLOY'.
(Other definitions for employ that I've seen before include "Make use of" , "Take on - recruit" , "Occupy" , "occupation" , "Hire; use" .)