Vessel indicative of rank? (4)
I believe the answer is:
ship
I believe this clue is a double definition.
'vessel' is the first definition.
(ship is a kind of vessel)
'indicative of rank?' is the second definition.
(as in an address like 'your ladyship')
(Other definitions for ship that I've seen before include "Large craft" , "Send" , "Navigable vessel" , "Large sailing vessel" , "Large boat, dispatch" .)