The Healer’s Mark is explained in the Healer template that I posted previously, but I’m re-posting just the text related to this new perk in a separate post so that it is easily searchable and shows up on the roadmap cleanly. There is no new information in this post, it’s just a re-posted excerpt from the Healer template.
Knowledge of the Healer’s Mark 
The Healer’s Mark is a secret known only among most healers: it is a modification of the flesh inside the patient’s body indicating a warning message to other healers. Although the exact form of the mark is not known, it might be an agreed upon crimped capillary in a particular place.
Every healer with knowledge of the Healer’s Mark will check to see if every patient is marked when first laying hands on them. If you harm or cheat or otherwise irritate a healer, then the healer has the chance to lay hands on you again, they are duty-bound to place the healer’s mark inside your body.
Once you are marked, no healer will heal you. The mark cannot be seen from the outside; a healer must lay hands on a patient to know if they have the mark.
It’s unlikely, but if a healer grew up isolated from other healers, they may never have learned the healer’s mark. This makes knowledge of the mark a 1-point Perk in terms of game mechanics, as it is a very minor advantage that might help a healer recognize an unsavory character.
The healer’s mark perk is only appropriate for healers, as without the healing power, the mark cannot be read.