Hello! YES there are several products out there that will reduce the adherence of spray-paint and felt-tip graffiti. Here are just a few:
MicroGuard from Adsil: http://www.adsil.com/products/graffiti.htm
Graffiti Proofer from SEI: http://www.seichemical.com/products/GPA-proofer_anti_stick.html
X-Off from Penco: http://www.pencoproducts.com/Pdfweb/XOffFly8.pdf
I do not know if any of the playground manufacturers are considering including these kinds of protective coatings on the products in the future but I will inquire and report back.
Also: while anti-tagging product is a definate option, it is also REALLY important to do the following if you find have griffiti problems:
1. Clean it up right away: the faster it's gone the less thrill there is for the vandal and the better those who continue to use the equipment will feal.
2. Be persistent: If you prove your resilience then the vandal may decide it's not worth the effort to re-tag over and over.
Good luck! And let us all know if you try any of those products -- I'd love to know how well they work.
Best,
Aron