I have an in-law unit at the ground level of my home. There are two locked doors in my space. The first is a closet where I store cleaning supplies, towels, and various items used to reset my Air BNB unit. The second is a door which leads to my private space.
I don't have any signage about what's behind the doors. I typically don't check-in my guests so nor would I explain what's behind these spaces.
These doors are both deadbolted with locks, so unless the guest was a locksmith or used a crowbar, he or she would be unable to access these spaces.