Random thought. Hair tattoos.
I have an idea for people who are bald but don’t want to get implants or other types of fake hair, yet are addicted to tattoos. What if, you could get your barber/tattoo artist to give you a tattoo that looked like a haircut. But you could get layers to it that would look like different hairstyles if you like that would change based on how the light hits your hair.
So imagine a design that encompasses a variety of hairstyles. Not necessarily a face tattoo, but a hair replacement.