I autocross my Boxster from time to time, I am in ASP now because of my 2nd cat delete pipes and UD pulley. My group said they didn't care if I stayed in BS but I felt funny about it.
I did make a BS magnet (and an ASP magnet) using a Porsche script type font, you are welcome to borrow from my letters/style if you want. Another member (Fred) helped me with these and so I would like to pass it along. I really like the Porsche script type letters.
I got the B & S from the Boxster S logo.
For this one I got the P from the Panamera logo, the S from the Boxster S logo, and I used a 4 to make the A. To me it doesn't look as good as the BS one.
My son has a vinyl cutting machine and would probably be glad to help you with some prototyping of decals if you don't have a cheap local source.