Originally Posted by big john

There are 98 cities in Los Angeles county and many of them have their own police departments. If not they contract the Sherriff dep't for law enforcement.
Each of these departments can enforce the way they choose, usually depending on complaints by locals. There are training rides which go through cites where the traffic laws are enforced much stricter than other areas. If enough riders piss off enough drivers the cops will hear about it.

As for groups going through stop signs, a group is not a single entity. If a group of cars tried to go through as one they could be ticketed. I know, it's silly for bikes but according to the law, each bike should stop at a stop sign. Most cops are not going to write a group but it has happened here.