Meh, I don't remember seeing that on the "IT Crowd".
I get people asking all the time if "The cake is a lie!" is a reference to me. How the hell am I supposed to know?! But I do find it interesting that there is rotary shaped graffiti in Portal (or so I've been told, I have not played it).
If you havn't played Portal you won't know what this thing is about the Cake.
In the game, the quirky computer promises you cake after you complete all the test chambers. She tries to kill you at the end, but you manage to escape and kill her... or so it seems. You'll then have to play Portal 2 to find out for sure.