It's been a week and two days since I shaved my head for St. Baldrick's. I highly encourage it.
One of the things I anticipated and have quickly confirmed is that people enjoy petting recently-shaved heads. I think it has to do with the texture. I used to love when people played with my hair (when it was long), and I definitely enjoy people petting the little bit of hair I do have now. Some of my friends joke that I was/am a dog-- I want to be fed and pet and taken for walks all the time.
One of the things I didn't expect was how much I would appreciate the question, "may I pet your head?" I'm not going to say no, so it's not a question that I have to actively consider. But I definitely appreciate people asking, at least the first time. It's a way of them showing that they understand that I may not want that physical contact.
That can be extrapolated-- ask permission. Get consent. It's important. It gives people their autonomy and the power to make choices about their own bodies and their own well being. And then respect their choices.