Register old design (4)
I believe the answer is:
logo
'design' is the definition.
(a corporate design)
'register old' is the wordplay.
'register' becomes 'log' (a log is a register).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'log'+'o'='LOGO'
(Other definitions for logo that I've seen before include "organisational symbol" , "Corporate symbol" , "Symbol or emblem used by organisation" , "Small emblem or device" , "Printed symbol as organisation's emblem" .)