A regular feature of tattoo left in gear (4)
I believe the answer is:
kilt
'a regular feature of tattoo' is the definition.
(kilts worn in the Royal Edinburgh Military Tattoo)
'left in gear' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' indicates putting letters inside.
'gear' becomes 'kit' (kit is a kind of gear).
'l' going inside 'kit' is 'KILT'.
(Other definitions for kilt that I've seen before include "Scottish garb" , "Scotsman's garment" , "Mac's skirt" , "Knee-length tartan garment" , "Scottish costume" .)