Book marks, one found after prize-giver’s heading off (5)
I believe the answer is:
obeli
'book marks' is the definition.
(plural of obelus, mark written on old manuscripts)
'one found after prize-giver's heading off' is the wordplay.
'one' becomes 'i' (Roman numeral).
'found after' is a charade indicator (letters next to each other).
'prize-giver' becomes 'nobel' (as in the Nobel Prizes).
'heading off' means to remove the first letter.
'nobel' with its initial letter removed is 'obel'.
'i' after 'obel' is 'OBELI'.
(Other definitions for obeli that I've seen before include "printing symbols" , "Printers' marks; be oil (anag.)" , "see below, we explain)" , "Textual marks" , "Signs of death" .)