“Reduced Beauty Treatment” covering small shop sign (6)
I believe the answer is:
'shop sign' is the definition.
(I've seen this before)
'reduced beauty treatment covering small' is the wordplay.
'reduced' means to remove the last letter.
'beauty treatment' becomes 'facial' (I've seen this before).
'covering' means one lot of letters goes inside another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'facial' with its last letter removed is 'facia'.
'facia' going around 's' is 'FASCIA'.
(Other definitions for fascia that I've seen before include "Shopfront signboard" , "Car dashboard" , "board above shop window" , "Flat strip on shop front for name etc" , "Surface over shop window" .)