Flashing headlights on your car is a handy signal for several purposes. It's a handy way to show people where you parked. If you have a security remote for your car, it's a way of telling you that you have just locked your car, or alarming if someone tries to break in. If you're driving, it's a courtesy to people who are passing you when they are pulling a trailer so they can know when they can pull over. And it's a classic way of warning oncoming drivers that there's a speed trap ahead.
Which is why flashing your lights can get you busted in Cleveland. A cop says "Basically they are obstructing our duty and our job to enforce the law."
Well cry me a river. I thought that the idea was public safety, not revenue for municipalities and excuses to jack up insurance rates. Flashing lights as noted above contributes to public safety, and I've actually had cops flash brights at me as a warning when I was speeding. And some municipalities have been notorious for funding themselves via speeding tickets or other predatory behavior against drivers passing through, such as Ludowici, GA, and Fruithurst, AL. Many others are listed here. (But the forces of justice are fighting back, and sometimes they win).
As for insurance rates, well...if traffic law enforcement were more uniform things would be different. And if you get a ticket and can't keep it off your driving record, you must not have tried.
Gosh, I seem to have wandered off topic - surely that hasn't happened before. Anyway, IMO this light flashing prohibition is pretty dim.