Gas sign in green letters (4)
I believe the answer is:
hess
'gas sign in green letters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hess that I've seen before include "Famous pianist" , "leading Nazi" , "Rudolf ..., Nazi leader imprisoned at Spandau" , "Pianist Myra, Nazi Rudolf ---" , "Cite as evidence" .)