It appears as if Bungie is trying to tell us that the first bit of meaningful Halo: Reach additional content isn't too far from release. In the studio's latest weekly update post, Bungie embedded two images clearly showing Reach's Gamerscore lifted to 1250 from 1000 and its achievements upped to 59 from 49--both of which are boosts indicative of a big content drop. Seemingly nodding to the pictures beforehand, Bungie led them with an all-too suggestive mention of additional new "stuff" coming down the pipeline in a possible second October update.
The aforementioned images were dropped in a section of the post dedicated to explaining how to install Reach to the Xbox 360's hard drive, while the talk of new "stuff" was placed after a meaty listing of things Bungie plans to change, tweak, or add into Reach's matchmaking (example: a SWAT-exclusive playlist, finally). These aren't exactly the places where one would tease DLC or other additional bits of content for a game as popular as Halo: Reach--unless, of course, one was attempting to circumvent traditional marketing or something--so it's possible this was just accidental or means nothing for the time being.
As Joystiq notes, Halo 3 ended up with an extra 750 Gamerscore, so what looks to be coming to Reach isn't shouldn't exactly strike you as a surprise. It'll be interesting to see, though, if DLC (or perhaps a points-adding update) hits as quickly as it looks like it could for the game.