Step down, not about to give autographs (4)
I believe the answer is:
sign
'to give autographs' is the definition.
'step down not about' is the wordplay.
'step down' becomes 'resign' (resigning is a kind of stepping down).
'not' indicates named letters should be taken away.
'about' becomes 're' (common abbreviation for 'with reference to').
'resign' with 're' taken away is 'SIGN'.
(Other definitions for sign that I've seen before include "Show" , "Signal, gesture" , "Pointer - indicate agreement in writing" , "Authorise with a name" , "Autograph" .)