Screen printed signs are made by applying ink directly to the substrate surface. Most often it is better to screen print signs if you are looking for a low number of print colors and a high quantity of signs (10 or more). Screen printed signs will also have more longevity 7-10 years on plastic and 15-20 years on aluminum.
Digitally printed signs are made by printing on vinyl and then the vinyl is applied to the substrate. It is better to digitally print signs if you are looking for a lower quantity (less then 10) or a high number of print colors (more than 4). Digitally printed signs will have less longevity at 5-7 years.