Olympia Historic District Freeway Signage

If you travel the I-5 corridor through Olympia, Washington you may have seen the brown signs that read “Historic District” attached to several regular DOT directional signs that are on the side of the freeway…  These medium brown signs are quite large and definitely get your attention as you are driving through the state capital area.  The signs serve as both advertising for the Olympia Historic District and also serve the purpose of helping folks who are looking to visit the district find their way.  We have seen similar signs in different areas across the nation - - we are wondering how the Centralia Historic District could get this type of signage on the side of the freeway leading into town going both north and south on the I-5 freeway???  Imagine the difference the signs would make…..  anyone know how to go about getting them???