Signify support (5,3)
I believe the answer is:
stand for
This clue is a double definition.
'signify' is the first definition.
('stand for' can be a synonym of 'signify')
'support' is the second definition.
('stand for' can be a synonym of 'support')
(Other definitions for stand for that I've seen before include "Mean" , "brook" , "support" , "become a substitute" , "Represent or tolerate" .)