A customer is asking us to warranty our signage for 24 months. Is there a standard, and if not, is two years reasonable?

There is no standard. The issues with signage are substrate deterioration and ink fade in sunlight applications, although a protective laminate with UV protection could double ink life. Latex inks are the most durable and could easily last two years outdoors. Vinyl takes a beating, however, which is why substrate manufacturers only guarantee it for one year when used outdoors. Indoors is a different story, as there are pigmented inks that can last years. Is 24 months reasonable? One can't say without knowing the inks, substrates, and UV intensity, but it does seem long, particularly for outdoor applications.