Law Against Purchasing Retired Road Signs in Washington?

[thefraze_1020]

A few years back, I went to a scrap yard to dispose of some metal, and saw a road sign there with a WSDOT fabrication sticker on the back. The manager of the yard said I wasn't allowed to buy it because a state law states that all retired WSDOT signs must be recycled and have their reflective surface removed.

I have hunted, but I cannot anywhere find this law. Is this policy true?

If so, is it legal to purchase retired road signs in Oregon, Idaho, California?