Design your own truck lettering by using paint or vinyl adhesives to design the letters. Painting requires the use of special car-appropriate paint mixtures that have silicone additives that allow the paint to last over time. Vinyl adhesives are available for customization through numerous online services that ship them.
Enamel paint mixtures made for outdoor use are appropriate for lettering the outside of a truck. The paint should be weather and wear-resistant to prevent problems with chipping and the letters fading or washing off. Vehicle stores carry already mixed paints meant for truck lettering jobs, or any other vehicle painting, in a wide range of colors.
First, wash off the truck's surface to ensure no dust or debris gets in the way of the paint job, then use a proper rubbing compound that wears away the protective outer surface of the truck's paint job so the paint lettering sticks more easily. If needed, use custom stencils, which may be ordered from online providers such as StencilEase.com or purchased at most local car stores. It is possible to perform the work by hand, provided you have a hand steady enough to avoid making small mistakes that are difficult to remove later.