A subway I was on recently had a sign in it offering helpful advice for various emergency situations.
Fire? Notify the crew member, exit to the next car. But don't pull the emergency cord.
Suspicious or criminal activity? Notify a crew member, who will in turn notify the police. But don't pull that cord.
Medical emergency? Notify a crew member, of course, and if you're qualified, inform them. But again, at all costs, don't pull the cord.
I just wonder, what exactly is the purpose of the emergency cord if you can't pull it for any emergencies?