The signaling server is a service that connects hosts and peers. It doesn't have anything to do with a dedicated server/host.
To have a dedicated server as host, you just need to have an always online server/computer, run your game on it, have it join a room first as host and leave it on.
You can distribute "client" versions of your game with host events disabled. This will ensure your peers can never join a room as host.
You can also use event conditions for your peers to ensure they do not join empty rooms, thus preventing them from ever hosting.