Hello and once again welcome to the Portal 1&2 Fan Group!

You might have heard about SteamPipe. This new distribution system has been introduced in Team Fortress 2 recently and it will also appear in Garry's Mod soon.
Something you probably didn't realize, though, is that one of the first games where SteamPipe was added was... Half-Life 2: Deathmatch. What's so interesting about this? Well, mostly the fact that the patch which introduced SteamPipe also added a new map to the game, named Halls3. You probably know what I mean, don't you? If it's the first map to be named Halls (and it indeed is), then why is there a three in its title? But that's not all. The patch which added the map appeared on April 3, 2013. We already have three "3"s*.
I appear to be one of the first people to discover this and therefore I encourage all of you to search for further clues. I also realize this might mean nothing at all, but... remember, E3 (2013 - even more "3"s) is coming!

http://combineoverwiki.net/wiki/Halls3 - the map's overview on Combine Overwiki

*HALF-LIFE 3 CONFIRMED (forgive me, I had to...)