It occurred to me that the skeleton key locking mechanism is not very secure (neither is the ignition, for that matter!).

Now, it really doesn't make a difference today, as nobody carries around a skeleton key nor would they know how to drive the car.

Anybody have examples of aftermarket trunk lock solutions available back in the day?

I have a 24 Coupe I inherited from my grandfather. He drove the car till 1954. He was a practical guy who added 21" Model A wheels to the car and as for as locking the trunk he welded on a hasp and keeper on the car to lock it up! It worked but sure wasn't original. I sure wouldn't do that to a car I was restoring these days but I had to respond to your post. It brought back some memories!

I was just thinking about the types that may want to carry something they would rather not be caught with (or have stolen). Being a prohibition-era car, there might have been some interesting home-brew solutions such as your grandfather's, or commercial products.