That's a vacuum breaker, and water should come out of it when you turn the faucets off. If water continues to come out long after you've turned off the faucets, you may have a freeze-damaged faucet that will require replacement of the shower faucet assembly.
__________________
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
Can you unscrew that tapered fitting that holds the hose on and take the internal bits apart for inspection? Might be as simple as something stuck in there. Vac breakers have little seals in them that can get messed-up by grit, scale, etc. Might just need a cleaning. Or, you'll find something freeze damaged...
This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.