SIGS, Page 4: Planning. 

It may be redundant, but it's good to have a plan before you go into a session. Not everyone is going to be an excellent subject going in, and there's a lot of inexperienced hypnotists out there still getting their bearings. 

Even if you have already gained consent once before, it is a constantly fluctuating experience. what might be okay yesterday might be off limits today. It's hard to predict. Even experienced hypnotists can slip up on this when your rapport with the subject has become very secure. 

A common BDSM safety system I've heard is the stoplight system. 
Green light: good to go.
Yellow light: feeling a little uncomfortable, skirting into rough topics.
Red light: stop immediately. it's time to perform aftercare.


of course these are very common phrases so it might be good to come up with your own. 

Know your limits, Trance responsibly. 

Art by Lager