@Levithian - unfortunately a partially closed door, with a curtain pulled across, is a fairly universal sign for "this isn't an entrance for the public - our staff \ workers are using this door, so we keep it open, but you aren't supposed to come in here, which is why the curtain is pulled across.
I used to work retail, and it was common to drop roller shutters across the doorway, to about head height, to allow existing customers to exit, whilst serving as a barrier to new customers entering. Whilst the curtain and roller door don't prevent anyone, its a fairly clear signal of 'don't come in here', and in all seriousness - a simple A-frame (which we know VRTP love) that says 'this way to the Aquaman Exhibition' with an arrow, or even "Aquaman Exhibition - OPEN".... it really is something very simple that would help prevent confusion in a place where guests check their brains at the door. Just because you can figure it out - doesn't mean the lowest common denominator can...