I've noticed several people stating that they use a Sharpie to draw on the black trim around windows of vehicles. I have done the same thing because it is easier than masking off areas and painting. The permanency of the ink has been an issue with me so I did a test. I used a scrap piece of stiff coated paper and put down a blob of black Sharpie as dark as I could get it, a blob of flat black acrylic by Tamiya, and a blob of black gloss by Testors. I set it on the back shelf area of my drafting table in the indirect sunlight for a month. Then I put new blobs on and took it into work and used a densitometer to measure the before and after blobs. The Sharpie faded visually and also by the numbers read with the densitometer. The acrylic faded a little, and the enamel hardly at all. Yes, this was an extreme test and I know hardly anyone would leave a model in the indirect sunlight, but I wanted to see what would happen. Especially since once the windows are painted and if the black trim fades, you're screwed. Personally I will use the enamel from now on even though it requires more work. I hope this helps.
Dave