Explanation/Reference:
The SIGN_POST table stores sign information that is used to generate driving directions. For example, a sign might indicate that Exit 33A on US Route 3 South goes toward Winchester. A SIGN_POST row might correspond to a physical sign at an exit ramp on a highway, but it does not need to correspond to a physical sign.
References: https://docs.oracle.com/cd/B28359_01/appdev.111/b28400/sdo_route_server.htm#SPATL904