What did he mean by this?

you just KNOW

...

know what?

you know

I know, you know........
.........

He's pointing at his jugular so I'm guessing it's an aggressive "fuck with me and I'll kill you" deal.

Never seen it in my life though.

WATCH IT OLEG

Underrated kino. I never see anyone talking about this.

check your pulse for hypertension, that shit kills

"A sign of major danger."
I also heard it's called "divide by 2" meaning "I'm going to snap your neck in half".

Being Russian myself I've never seen this sign. It's either very obscure criminal sign langauge or just made up.