There is no signalling, except for one marker in the middle of the longest stretch of single track rail between turnouts. Whoever reaches it first can continue, the other party has to go back. Though apparently, you can see whether the other car will be first, and wait.
Also, you don't really need forks, because are light enough to be lifted off the tracks. Some pull them up on special car trailers.
It's a unique situation in Germany, and one that works for a small community where everyone knows everyone else.
The cars are not only privately owned, but handmade with wood and motorcycle parts.
There are a couple of safety rules, which are enforced by a permit you get from the mayor of the Hallig (island), and if you break the rules too often, it gets revoked. Which has happened only one time so far, apparently.