Manatee, you have to sign in with a buddy. Learned that lesson the hard way... three man dive planned, two of us showed up together and drove back to wait at the spring for the third person, who never showed up, because she couldn't get in without a buddy. We felt terrible but I've never forgotten the lesson!
Alexander, I believe you can sign in by yourself.
At Manatee, I've had rangers interrogate me because I had cave diving gear but was only diving as an OW diver, and they thought doubles and reels were taboo for an OW diver.
At Alexander, I've been stopped on the path to the water and been asked to show my dive bracelet. Mind you, I was in doubles, and it was very hot out. Also, I had put the bracelet on my ankle just for kicks and giggles. Wasn't fun balancing on one leg to remove a boot to show the lady I had indeed registered.
But, I was alone, my buddy was already getting in the water, and she didn't ask where my buddy was.