911 is not just a number. The first thing which comes into our mind is nine eleven. Also, 911 is the emergency number in America. And of course a well-known Porsche line.
Against the European registration of this sub-brand of Porsche a German (!) company filed a cancellation action. This company contested that 911 is a distinctive trademark for various products and services. Some hilarious arguments are brought in the case: 911 is a date, or could be a calender, or a radio frequency. Moreover, being a sub brand for cars, this trademark only refers to cars and cannot act as a trademark for for example cosmetics. Finally, the fact that 911 is the emergency number is also mentioned. An emergency number in America can not be a valid trademark in Europe!
The OHIM examines the request and states that a number can be a distinctive trademark, provided that it does not describe the products. So, the number 15 for clothing was rejected as it could it can indicate a measure. But 911 had at the time no meaning at all with the relevant public. Therefore, the OHIM rejects the request with a speeds that reminds us of a Porsche.