Lt. Commander Eddington announces "Captain on the bridge" when Sisko first boards the Defiant. This appears to be irregular, as nowhere in the history of The Original Series, The Next Generation or Deep Space Nine (until this episode) is a captain given such treatment. previously, this sort of formal honor had been reserved for Ambassadors and Starfleet Admirals. Perhaps he says it just to commemorate Sisko's new rank, though.
Depending on the stardates, the phrase "Captain on the bridge!" is in fact spoken aloud in the Next Generation episode "Chain of Command Part I" to acknowledge the arrival of Captain Jellico onto the bridge. This however may or may not come before the DS9 episode.