Unsigned routes can be one of two things: first, a highway may be primarily signed with one designation (such as a U.S. highway) but also carry another designation (such as a state route). These hidden designations include U.S. routes that silently merge onto an Interstate highway and hidden state route control numbers used by various departments of transportation throughout the country. An example is U.S. 87, which is the unsigned counterpart running alongside Interstate 25 in Colorado.
A second definition of an unsigned route is a route that may be maintained by the state and has a state route number but is not signed in the field. An example is the stretch of California 1 near Emma Wood State Beach, which is an unmarked state route.