The stripes on the officer's shirts indicate rank. Two chevrons are police officer III (Sometimes called Corporals), a police officer III +1 has two chevrons with a start beneath, three chevrons is a Sergeant I, three chevrons with a curved up facing stripe is Sergeant II (sometimes called Staff Sargent). A Lieutenant would have a vertical bar and C a Captain would have two vertical bars.
Nyla puts one of the attackers in a textbook rear naked choke which is now illegal for officers to perform after a ban put in place following national attention of the George Floyd case several months after this episode aired.
When Jackson has his gun out at the heist location, the slide is locked open.