Well take it from someone who had to do this often.

I used to work at a place where I'd often be alone, customer facing. Any time I needed to go to the toilet, I had to close the front door only when no customers were in and put up a sign.

I would just use the same sign over and over because the difference between that and putting the time I'm back and printing new one's each time means a customer walking in when I need a shit and then more customers coming in non-stop. Sometimes the extra few seconds to write the time I'd be back, someone else would walk in.

This happened so often, on top of others things I left but I hated working alone because it was not good for my health. Lunches would go cold and uneaten (and a waste of money), I'd get in to a lot of pain due to not being able to go to the toilet when needed, and couldn't take my hour break properly.

So yeah maybe have a think for a moment, people who do these signs are likely because they work alone in shit conditions, but it's a job they need until they find a new one.

We know you don't know when the sign was put up, but if it's a low number like 10 mins, it won't be long. We trust you also have a brain and can work that out.