@Brookside, same here! There's no sign like that in any of my doctors' offices! It's an unmentioned "suck it up and wait" attitude.
Which leads me to the one time I walked out on a doctor, and let the receptionist & nurse know that I would not be returning. When my oldest daughter was an infant, 28 years ago, I was referred to the most arrogant, self-important, judgmental pediatrician known to man. Every appointment was at least a 45 minute wait, and then once I finally got in to see him he would tell me how busy he was and rush through my appointment. One time I left in tears because I had asked a question about weaning my daughter off the breast and he berated me for 10 minutes about what a horrible mother I was for not continuing until she was a year old. She was 6 months and I was going back to working full-time. The next appointment I sat waiting for an hour, I went to the desk only to be told "he'll be with you soon". After another 30 minutes I went to the desk and asked again, the b*tchy receptionist turned to me and said "He will be here when he gets here, he had an emergency out of the building!" As she was saying this the nurse walked up nodding her head in agreement, so I looked at both them and said "You mean to tell me I have been sitting her for 90 minutes and he isn't even in the building, and you didn't feel the need to offer to reschedule?" No response except glares, so I told them forget it, I'm done here, I will be transferring to a new pediatrician who actually has time for his patients, with a staff who understands that everyone's time is important, not just the doctor's.
Years later I told this story to an acquaintance and she exclaimed "Was it Dr. So-and-so? And I said "yep!" and she told me she had the exact same experience with him. I was glad to hear it wasn't just me.