Thanks for that follow-up, Fab Fifties Fan. Fascinating stuff!
And you reminded me of something. Twelve years ago I spent a week house-sitting for some friends of mine in the hills above Sunset and Fountain (Franklin Hills). The owner believed that his house had been used at one time as an illegal gambling parlor. The ground level of the house had been modified at some point such that there were no fewer than six doors leading outside, most of them on the sides of the house. These were presumably added so that several people could make quick exits in the event of a raid.
At the front of the house, there had been added near the eaves a curious little figure of an owl. The owl's eyes were small red light bulbs, with the switch for the eyes on a wall inside. (They were still functional when I stayed there.) In theory, the owl's eyes would have been illuminated as a signal to let patrons know that it was safe to come inside and gamble.
Here are two photos I took when I was house-sitting. In the first photo, the red circle shows where the owl is situated.
I've also heard that there were at one time gambling ships located three miles off the coast in Santa Monica Bay.