-When you run HL and other games in window, so you can immediately start new map if good idea occurs in your mind while playing
-When you make a user-modified version of Linux, that runs Hammer all the time and the background is actually a Hammer window
-When you steal the HL2 source, so people can keep mapping for HL1 and your maps are always recent (oops, I think I shouldn't have said this one...
)
-When you put Lambda as your My Computer icon and call you harddrive containing HL "Half-Drive"
-When you logged on 28 diffirent machines just to vote for HL at the GameGrudge (planethalflife)
-When you have remade all HL SP maps without decompiling (man, thats alot of work)
-When you're a modteam member
-When you have a hammer drawn on all your notebooks
-If you think that the communist coat of arms is inspired from VHE (Worldcraft)