Sign of implement (7)
I believe the answer is:
execute
I believe this clue is a double definition.
'sign' is the first definition.
(I know that execute is a type of sign)
'implement' is the second definition.
(I know that execute is a type of implement)
'of' is the link.
(Other definitions for execute that I've seen before include "Complete - implement" , "ice" , "Carry into effect" , "shoot" , "Inflict capital punishment upon" .)