What should the DPI be for a clear print on a sign?

As a general rule, the larger the sign, the lower the required DPI. For small products like a 4" x 4" sign, a resolution of 300 DPI or higher is ideal for sharp results. For larger products—such as a 33" x 81" retractable banner—a DPI of around 100 is typically sufficient, since they're viewed from a greater distance.