Not to be rude, but in general, if you outright say it, it's not true. (In years of working computer administration and security, I have never once met a person who called himself a "1337 haxor" that actually deserved anything resembling that title. The only people who actually deserve that title know it's stupidity and avoid it like the plague.)
The only seemingly egotistical geek license plate holder I've ever seen that WASN'T an ego trip was a Mercedes SLK with a license plate holder reading "Mr. Linux" on top, "King of Geeks" below. (The custom license plate was a fairly sedate one mentioning fatherhood.) Yup, Linus Torvalds was in the driver's seat.
I have continued to see the car around town a few times over the past few years.
(edit: Removed the actual content of his custom license plate for privacy reasons. After all, Oregon's driver and vehicle registration database is publicly accessible.)
Not to be rude, but keep comments like that to yourself. I do not know the first thing about hacking, but if I had a vehicle worthy of putting it on I would just because its funny and its a joke. Anything with 1337 in front of it is a joke, and you should take it as such.
I'm on the verge of getting an IT job finally after years of schooling, so hopefully I'll be able to post a new ride with a new tag soon