If you have a Generation III Prius (2010-present) 15 inch wheels, you can pop off the UGLY wheel covers to release the alloy beasts underneath. Except - you'll have a hole in the center of the wheel that begs for a decorative cap. These are based on precise measurements of Toyota part #42603-52110.
These feature the Greek letter Theta, which has represented the idea of "Ecology" since the late 1960's http://en.wikipedia.org/wiki/Ecology_Flag
Also fits Yaris, Vios
Nylon is NOT UV stable. For maximum longevity and downright good looks, you will want to paint this object. Acrylic paints with a glossy topcoat are a proven method of painting objects printed using Selective Laser Sintering.
Shapeways has a tutorial here: http://www.shapeways.com/tutorials/painting3dprintedsls
And a blog entry here: http://www.shapeways.com/blog/archives/129-painting-your-3d-printed-models.html
Further, you can locate the recommended Tamiya paints here: