My 3-year-old DD weaned at 2, and she still does this. We have a couple of rules: no touching or pulling my shirt up in public or in front of windows. No pinching. No rubbing. She can put her hand, or lay her head, on my breast, but it has to stay still. She is growing out of it very, very gradually. When she first weaned, she had to fall asleep with her head on my breast every night. Now it's just a few times a month. Honestly, I think my breasts are her security blanket. So I don't let her do anything that would drive me nuts, but I'm not going to totally ban her at this point.
We have had several talks about my body being mine and her body being hers and just as I respect her wishes about her body she must respect my wishes about my body. If she can't respect my wishes, then I won't want to be around her. And I enforce that. If she pinches, I give her a warning. A second pinch means I'm getting up and going somewhere else, unless she apologizes promptly and says she won't do it again. If she does it a third time, I am OUT of there. That hasn't happened more than once or twice.