From California Traffic Control Device Committee member John Ciccarelli, who says these come from the Caltrans signage design staff. These aren’t the officially approved designs (yet) but will be similar to what will eventually appear in the California edition of the MUTCD, which should be published within the next few months.
The sign committee chose the “PASS” wording on purpose to clue motorists in that they should drive as if they’re passing another vehicle when they pass a cyclist.
No Federal sign exists as of yet. As I noted last week, Utah and Florida also have three foot law signs of their own.