Indication one’s engaged in call (4)
I believe the answer is:
ring
I believe this is a double definition.
'indication one's engaged' is the first definition.
(as in an engagement ring)
'call' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for ring that I've seen before include "Besiegers' formation" , "Circle that's square for boxers" , "Call - cartel" , "place for fight" , "Encircle; arena" .)