Look at LinkedIn to see if long-time employees have gotten promotions. See what their turnover is like (if people are dropping like flies, particularly in a certain division/team, you can bet it's not a very safe place). Also see what kind of side projects develop out of the team. If you see tons of internal tools and useful "hackathon"-esque features, you can bet there's quite a bit of autonomy to be able to develop those kinds of things.