Nothing beats professional engaving, which can be affordable if you have a lot done in one go, but laser printing on transparent adhesive film can come quite close and you can keep changing your mind! The trick is to match any existing engraving font style and size carefully, and (since you are normally trying to stick to a convex or concave button surface) to cut the carrier film down as small as possible - ideally to just around the lettering. A second layer of film over the printed film protects it from smudging or wear.
Here is one of mine.
- Adrian.