(a) An adverse claim must be filed with the authorized officer of the proper office where the application for patent is filed or with the manager of the district in which the land is situated at the time of filing the adverse claim. The claim may be filed by the adverse claimant, or by his duly authorized agent or attorney in fact cognizant of the facts stated.

(b) Where an agent or attorney in fact files the adverse claim he must furnish proof that he is such agent or attorney.

(c) The agent or attorney in fact must sign the statement of the adverse claim within the land district where the claim is situated, stating that it was so signed.

(d) Each adverse claim filed must include the processing fee for adverse claims found in the fee schedule in § 3000.12 of this chapter.