Yes, it's an unloading barrel.
As Tam says:
Thank you, Indy 1500! If you're going to mandate that I coonfinger my loaded heater in the name of safety, good manners would dictate that you provide me a safe backstop against which to do so. Thank you, thank you!
If only more places that mandate "clear your guns before entering" did that. It really is basic manners, if you mandate that people have to do X before they come into your establishment, provide a way for them to safely do X.
Note that the majority of Gun Free Zones do not have any sort of lockers or security, real security, for their little clubhouses.