Harold only has saintly sign (4)
I believe the answer is:
halo
'saintly sign' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for halo that I've seen before include "Saint's headlight?" , "overhead lighting?" , "Ring of light (signifying holiness)" , "that could make one light-headed?" , "Aura round admired person" .)