Yes there are signs. I'm assuming it's illegal because that road is always backed up with people waiting to turn in to get to the school to drop their kids off.

I'm assuming they don't want people turning left out of there and making the traffic worse, but I can't help but feel there are better ways to solve this problem that pay a cop to sit there and yell at people over his intercom.

He never bothers to get out and direct traffic and help solve the problem, just yells at people and gives tickets to people who can't hear him/turn left anyway.