47 CFR § 68.300 - Labeling requirements.
(a) Terminal equipment approved as set out in this part must be labeled in accordance with the requirements published by the Administrative Council for Terminal Attachments and with requirements of this part for hearing aid compatibility and volume control.
(b) All registered telephones, including cordless telephones, as defined in § 15.3(j) of this chapter, manufactured in the United States (other than for export) or imported for use in the United States, that are hearing aid compatible, as defined in § 68.316, shall have the letters “HAC” permanently affixed thereto. “Permanently affixed” means that the label is etched, engraved, stamped, silkscreened, indelibly printed, or otherwise permanently marked on a permanently attached part of the equipment or on a nameplate of metal, plastic, or other material fastened to the equipment by welding, riveting, or a permanent adhesive. The label must be designed to last the expected lifetime of the equipment in the environment in which the equipment may be operated and must not be readily detachable. Telephones used with public mobile services or private radio services, and secure telephones, as defined by § 68.3, are exempt from the requirement in this paragraph (b).