I'm not sure about the Sig paints as I have never used them on plastic. However, I would try the Testors brand lexan paint for r/c car bodies on the canopy and plastic top.
Tamiya makes a plastic safe paint as well. Also, regarding the r/c car body paint, try it on a scrap piece of plastic first but I think it will fine. Oh before I forget, the r/c car body paints go on flat so you would most likely have to do some color sanding and add some clear coat. I've used those paints on some plastic model cars with good success but I'm not sure what kind of plastic your working with.
Hope this helps,