What do the "slashes/tallies" mean on your profile online?

[Hayzie]

You see this on the CSS. Some people have 1, 2 or more. What kind of ranking symbol is this? Or is it a streak? I can't make out the symbol as I'm playing via gamepad.

I checked the in-game's manual (which is cool), but I didn't see it (okay not cool).

 

[Chibij]

I believe it's the number of KOs that person have gotten during that session.

 

[Hayzie]

I believe it's the number of KOs that person have gotten during that session.

Neat.