Slow walker ignoring learner driver’s signal (5)
I believe the answer is:
amber
'signal' is the definition.
(I have seen 'Cautionary signal' mean 'amber' so perhaps 'signal' could also mean 'amber')
'slow walker ignoring learner driver's' is the wordplay.
'slow walker' becomes 'ambler'.
'ignoring' is a deletion indicator.
'learner driver' becomes 'l' (I've seen this in other clues).
'ambler' with 'l' removed is 'AMBER'.
(Other definitions for amber that I've seen before include "gemstone" , "Middle light" , "Fossil resin - bream (anag)" , "Warning to traffic" , "Prepare-to-stop signal" .)