Do you turn off your phone when you see a sign that says "Please turn off cell phones"?

I walked into the optometry waiting room and there were 5 or 6 big signs in the room stating the above and as soon as I sat down I glanced around the room as I got my phone out. About half of the people in the waiting room were on their phones that I could see and some had their backs to me! Under what circumstances do you think its acceptable to refuse this request?