Here's a .sig I thought cute:

There are 10 types of people in the world: those who get binary and those who don't.

Of course, I don't "get" binary but when my three-year-old asks me to double numbers beginning with 2, I'm glad I can do it without thinking too hard:

2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, usw.

"2" - It's a Magic Number.