So, only the 'owner' or someone working under the apparent authority of the owner can post valid 30.06 signs.(b) For purposes of this section, a person receives notice if the owner of the property or someone with apparent authority to act for the owner provides notice to the person by oral or written communication.
Since the 'owner', eg, the fed, just stated in law that they're cool with allowing guns to whatever extent the state law allows, obviously anyone who posts a sign is not acting with the authority or knowledge of the 'owner', so they would be invalid.
That would be similar to if I I owned a large business. Say that I was the owner of a large restaurant (not a 51% facility).
Say I posted in the newspaper, that I fully allow & support the public to carry concealed weapons on my property.
Seeing my newspaper post, a manager in my restaurant, unknown to me, posts 30.06 signs.
Obviously he was not acting under my authority, and my authority on the subject was well published, it should not hold water in court.
My interpretation :)