Many PvE players don't know what WvW is. They've never been in it, haven't clicked on the icon, don't know what the B key is mapped to... So why not advertise WvW like seasonal events are advertised?
I know during downstate, etc. events WvW is advertised, but we need fresh blood -- so outside of events, just put up a "Try WvW today! You're on server ". May as well alternate with other game modes.