We have used Sharpie UV resistant markers to make labels on 12-inch sections of 1/2-inch PVC pipe and found that the writing fades in sunlight within a year so that it is impossible to read. Does the writing produced by a Sharpie last longer on the plastic of water bottles?
Yes, we have found most pens to fade quickly. Some of our garden centres carry a pen called "Planters Pride". We find this one to last 2 or 4 years - dependent on exposure. For seedlings, we place the tags not quite vertical (name facing down some) and with the writing on the north side. Using this down and north method, we get 4 years out of a tag. By then, the seedling has shown itself with blooms, and we have made the keep/not keep decision and no longer need a tag, or have made a permanent one.
However, I've gotta try AnnaZ's pen.