These signs have been there since I can first remember in 1968. Grew up in Vancouver, USA and we would travel to Fort Lewis on a regular basis as my dad was Retired Army.
They tried years ago to get them down and lost. Signs are outside the I-5 Right of Way so I don’t see where Federal Highways has any say to direct WSDOT to remove or have funding withheld.
As long as I can remember any time the feds did not get their way in Nebraska the first thing they always did, always being the word there, was threaten to take away highway funding.