A long time ago I did an internship at a marketing firm that did work for Subway Sandwiches. As such, it was considered a fireable offence to bring any other branded "sub" into the office.
Ugh. That's just so stupid. What if they do work for a bank, automobile manufacturer, clothing designer, etc? Are the employees obliged to then buy new clothes, cars, hide their branded debit cards in the cafeteria?
Edit - to answer my own question I searched Google and found this:
I doubt that the majority of people that work for Mercedes drive their cars.
 http://www.expo.be/en/jahreswagen/index_nl.phtml, lots more info if you read German.