[JameRetief]

I don't believe so. Only the word Porsche itself is a trademark.

[Constitution Day]

Hmmm... I'll take your word for it.
I still think they'd be a little miffed if I started up the "Joe Blow Car Co." and came out with a "911" model.

[Bush2000]

I don't believe so. Only the word Porsche itself is a trademark.

Actually, it depends upon whether the branding of a product or service causes confusion. The courts typically uphold trademark protections against products or services in the same or complementary markets. If you were to create, for example, a shampoo named 911, the courts would probably not give Porsche trademark protection. However, it is my understanding that the courts prevented a company that was producing auto floor mats with the labels "911", "944", etc from doing so. This seems like a reasonable thing. Porsche invested in its trademarks. It deserves to not have them devalued by third parties.