Course of action: Take the doors off the cabinets, remove the stencils, clean the mirrors, reinstall the doors.
Square tip screwdriver
Single edge razor blades
We removed the screw on the door support then removed the top screws on the hinges. Placed the door face up to the table and removed the stencil using a single edge razor blade. Next we cleaned the mirror with Windex and used the razor blade again to remove any traces of the stencil we missed. Next we cleaned the mirror again with 70% alcohol which removes any streaks left by the Windex. Lastly we reinstalled the cabinet door.
Maybe it was plain luck or the fact that the stencils were on the mirrors for over 20 years, either way it took less than 30 minutes to complete each door.
After completing the cabinet doors project the living room had the illusion of being much larger than before. We like the outcome very much and plan to remove the stencils from the overhead cabinet doors that are in our bedroom in the near future.