The PvP Reward flags should be a Permanent piece of equipment, that shows up in both WvW and sPvP.
The flags would NOT be in reward chests, but instead granted at certain ranks so that finishing a player shows off what sPvP rank you are. (Or were, if you equip an older one)
This would me sPvP ranks more rewarding and interesting, as well as a guaranteed reward instead of constant random ones.