Call for sign of commitment (4)
I believe the answer is:
ring
I believe this clue is a double definition.
'call' is the first definition.
(synonyms)
'sign of commitment' is the second definition.
(as in a wedding ring)
'for' acts as a link.
(Other definitions for ring that I've seen before include "Piece of jewellery" , "Hoop" , "Arena; jewellery item" , "item to be fingered?" , "Telephone - as bells do" .)