During the closing credits Philip Rahm, a professional cellist who plays the German, plays the show's theme song on cello.
The doorbell chime of the German's home is "The Chicken Dance"
In the background of Roy's tiny apartment, a sheet of paper can be seen taped to the wall that says "Home Sewing Is Killing Fashion and it's Illegal". It is a geekish reference to an early anti-piracy campaign of the British Phonographic Industry (BPI) from back in the 80's. The British music industry trade group spread the slogan "Home Taping Is Killing Music". With the rise in cassette recorder popularity, the BPI feared that the ability of private citizens to record music from the radio onto cassettes would cause a decline in record sales. The logo, consisting of a Jolly Roger formed from the silhouette of a Compact Cassette, also included the words "And It's Illegal". Music and video "piracy" are of course staples of the geek lifestyle.
In one scene with Jen, you can see Moss reading 'Mustard Magazine', a cult comedy magazine that IT Crowd writer Graham Linehan reads in real life.
In one scene, Roy is wearing a shirt advertising Pink Floyd's 9th studio Album, "Animals". In Episode 4 of season 1, "The red Door" Roy sings "Another Brick in The Wall Part 2" From the groups 10th studio album "The Wall". These implies that he is a Pink Floyd fan.