Administrative Instructions under the Patent Cooperation Treaty

 Section 107
Identification of International Authorities and of Designated and Elected Offices

(a)  Whenever the nature of any communication from or to the applicant, from or to any International Authority or, before national processing or examination has started, from or to any designated or elected Office so permits, any International Authority or any designated or elected Office may be indicated in the communication by the two-letter code referred to in Section 115.

(b)  The indication of a receiving Office, an International Searching Authority, an International Preliminary Examining Authority or a designated or elected Office shall be preceded by the letters "RO," "ISA," "IPEA," "DO," or "EO," respectively, followed by a slant
(e.g., "RO/JP," "ISA/US," "IPEA/SE," "DO/EP," "EO/AU").