There are more than just two kind of people

Z
 
(If you're not sure what this means, it's the Greek Letter Zeta, which, in mathematics, has a value of 7.)

So world war Z is..?

I'm a mix of 4 and 2. Combine those and there's me : number 5.

same here. I cross my sevens with the little overhang thing

Binary, clever!