I suppose you could tell the doctors because they were in scrubs? In general, it would be hard to determine the profession of your customers.
No, because they were staying at the hotel I was working at, so maybe in 30 years they have gotten more stingey with tips

....Doctors were the worst tippers...waitresses and bartenders were the best...come to think of it, I got a few "Jehova's Witness" type cards left as tips in lieu of cash from some Ministers...my soul appreciated it, but my gas tank was still on fumes......anyone who has worked for tips is usually a good tipper, my minimum is 20% and if the service is off, I start to deduct from there.