Whenever somebody is offering a signing bonus, I start to hear that little voice. I'll readily admit that it's not necessarily true of all situations, but if the location is good and the job is good, why are they offering a signing bonus? I'll also admit that what I view as a good job and a good location may not be what you view. And your priorities may be different than mine.
I've heard a lot of the "Watch out for the management companies like_____." Fill in the blank with any AMC--Sheridan, NAPA, etc. I don't hear a lot of, "I work for _______ AMC, and I love my job." There is a guy on the Sheridan thread who has some decent things to say about Sheridan, and I'm glad he has, because I don't know if a lot of the people who are saying things about the AMCs have direct experience with them. That doesn't mean that what they say isn't true. Also, I'm trusting that they anonymous guy on an internet forum is actually speaking the trugh. Caveat emptor.
One thing I have observed is that the AMCs like Sheridan and NAPA seem to be advertising the same jobs over and over for months if not years. Go back through some of the old journals or Anesthesiology News and see if those vacancies from a year ago are still vacant. Again, if they're so good, why are those jobs going unfilled?
I'd have to have a very compelling reason to work for an AMC, like I absolutely MUST be in a specific location, and AMC jobs are all there is. But your reasons may not be mine.