Closed is such hard word to understand

I work opening on Sunday. People NEED to get to teh Interweb on Sundays, so for the hour or so before the doors open, people try the door, notice it's locked and start knocking. It's not that we try to hide the hours--there's a sign right on the door that either says OPEN or CLOSED. I often can't see the face of the knocking person (to see if they are a volunteer who works before opening) because it is obscured by the sign. I guess that people see lights on and people scampering around pulling holds and assume that we MUST be open.