Unless it rains a lot, you should wash your outdoor sign gently with a soft rag and warm (not hot) water once every  year or two. For High-Density-Urethane (HDU) signs, the paint should retain its color and brightness for seven years or more (Matthews Paint Company guarantee).After that, minor fading may occur if the sign's face is in the full sun, especially for red and blue colors. . We put two coats of 1-SHOT Oil enamel Sign Paint or Matthews automotive-type MAP acrylic polyurethane paint (costs $200/gallon) to provide very long-life with minimal fading. We also coat every sign with 2 coats of MAP clear-coat for additional UV , moisture and graffiti protection. After 7 years, if you wish , you may wish to retouch fonts with any oil enamel with matching colors. HDU signs will never rot or crack from rain, snow, ice or freezing/thawing, that is why we always recommend them for painted outdoor signs in the weather.

For outdoor wood signs, whether painted or stained,  more maintenance is required. Once a year the sign should be expected for tiny cracks, and if found, they should be filled in with Bondo or plastic wood filler and the paint retouched. Our painted and stained outdoor wood signs will last over ten years with good maintenance. The most damaging situation is for cracks to appear in the surface of the wood, front or back, and water to get into the interior wood, which will cause rot and cracking of the substrate. Outdoor signs subjected to in rain, snow, ice and freezing/thawing are affected the most. Repainting and touch-up for these signs is the same as HDU described above.

Clear-coated natural wood (stained, not painted) wood (Cedar, Redwood, Mahogany) signs require annual or bi-annual clear-coating in addition to possible crack filling. Think of a varnished wood boat; they require 10 times more maintenance to maintain their appearance than a fiberglass boat. The same is required of natural clear-coated wood signs. After staining them, we clear-coat them twice with Marine Spar UV resistant varnish,  but eventually the varnish wears off due to UV, rain, sprinklers, people touching them, etc, and they must be given a new coat of varnish before the wood is damaged. Once damaged, the surface must be lightly sanded before new coats of Spar Varnish is applied.

Indoor signs or outdoor protected signs (under a building overhang, for example) require very little  maintenance, and will last several decades,  Indoor wood sculptures have lasted 500 years without damage, as long as temperature and humidity levels  are reasonably controlled.