What's the best way to renew worn off letters on a laptop keyboard?

The white lettering on the A and S keys is gone. The top half of the letter E has disappeared as well. How clunky are those stick-on letters for laptop keyboards? Is it better, instead, to use some sort of pen to re-letter keys by hand as required? If so, what sort of pen works? What’s the best way to repair the wear on key faces?