1. Wings and things.
The deatailed-minded may notice this winged emblem occasionally popping up on military attire. It's actually a well-known trademark of Clamp, and can be found littered all over their most recent works, including Tsubasa Chronicles, XXXholic, Cardcaptor Sakura, and Kobato. Since the characters of Code Geass are designed by the four-women talent team, this is just one of the ways that they're given credit where it's due.
2. Italian Britannian.
C.C. doesn't eat just any old pizza. In fact, she has a very particular taste in ones made underneath the famed red roof of Pizza Hut. Further evidence of cross-marketing can be seen on a limited-time pizza box in Japan which sported Zero on the cover. This form of blatant marketing only bared itself in the first season, never to be seen in R2.