The number is added to the name "you" to distinguish between one client and another. It prevents you from thinking you are scoring frags that someone else got. That's my guess anyways.
I'll explain a little better:
I am playing a 2v2. There are four players- Mael, casp, Imp, and "you"(Not you but a player named "you"). If "you" frags casp, the console will show the message "you fragged casp" on all other clients' consoles, thereby fooling them into thinking they fragged casp when they didn't.
The number is added to prevent such confusion but only for the name "you".
I'll explain a little better:
I am playing a 2v2. There are four players- Mael, casp, Imp, and "you"(Not you but a player named "you"). If "you" frags casp, the console will show the message "you fragged casp" on all other clients' consoles, thereby fooling them into thinking they fragged casp when they didn't.
The number is added to prevent such confusion but only for the name "you".