If the eyelashes are soft and any color other than black, the doll is PM. Mattel dolls all have shiny black lashes. If there are any tags, PM ones say made for Pleasant Company, Mattel ones say made for American Girl. I have a PM and a Mattel Felicity as well as a PM and a Mattel Kirsten that all have the artist mark behind their ear, so I don't think that is an accurate way to tell the difference. If you know when the doll was made, anything manufactured prior to 1998 is PM. For me the only thing that I have found "for sure" is the eyelash differences.
~Stacie