In most instances, it is possible to remove vinyl lettering with no residual damage to the applied surface. While this is typically the case, different substrate materials can react in different ways, so if you're unsure of the resulting reaction, it's important to test an inconspicuous area of your surface before applying the following techniques to the entire area. The upside is that most surfaces, including vehicles, respond well to the vinyl removal technique outlined below, with no resulting damage to the surface.(Note: When working with decals that have been in place for a significant length of time, there is the slight possibility that the paint around the decal will appear discolored or faded upon removal. Usually this only occurs in cases where the decal has been exposed to the sun for extreme periods of time. This significant sun exposure will result in a tan line effect on the surface, whereby the unexposed area under the decals will appear nice and shiny next to the faded, exposed surface.)
In the case of an old wooden sign, where the paint is already chipped and peeling, it is important to keep in mind that the paint will most likely peel off with the vinyl letters when you remove them.
The following step-by-step instructions provide a good basic plan for removing vinyl decals, stripes and letters.