How to Deal with Early Morning Honking

It's illegal to honk your horn unless it's an emergency. Use law enforcement. Google the question to get specific answers, I could not cut and paste the article here.

Not true at all about it being illegal unless it's an "emergency." From the CA DMV handbook: "Use Your Horn
Only when necessary, to avoid collisions.
To try to get “eye contact” with other drivers. You may tap your horn to alert another driver who might turn in front of you and cause a collision.
On narrow mountain roads, where you cannot see at least 200 feet ahead of your vehicle."

Please don't bother the police with someone honking their horn for a reason you are not sure of.

Set your alarm, go outside, get the car make, model, color and a description of the driver. Call the non-emergency county sheriff phone number and report them.

Have you actually seen this or are you going by sound alone? Is the car really just driving by or is it stopping to pick up a neighbour? If you knew that you could contact your neighbour and ask to have the driver call or text him/her. Or better yet, they could be ready on time and wait for their ride outside and save the driver from waking up the block. But you'd have to forgo the Trumpian attitude of attack first and be nice later.

I remember reading in local ordinances that, yes, it is illegal to use your horn unless your intention is to alert a fellow driver and such like. Honking a vehicle's horn to let someone know you've arrived or are leaving is stupid and obnoxious, particularly in the early hours of the morning. Many years ago I had the same thing happening across the street from my house. In my case, I should have told the local beat officer and he would have talked with that girl I am certain. Instead, I confronted the teenage driver, hoping she would be kind and understanding. She was there to pickup her schoolmate. After I asked her to please stop with the honking, she then honked and honked even more every Mon thru Fri morning, and made a point of honking as she was picking up and dropping off her friend, whenever. Looking back, I could have tried speaking with my neighbors but, you know . . . heaven forbid you speak to neighbors about their noise or their friends being noisily obnoxious.

Probably also falls under the disturbing the peace statutes. The definition is usually a sound that is out of character for the time and place. But you might have to keep after them to enforce it, and also call your local politico and ask them to help you with the police.