Section 300.143 - Facilitation of enforcement(a)General. Persons aboard fishing vessels subject to this subpart must immediately comply with instructions and/or signals issued by an authorized officer of the United States or Canada, or by an enforcement vessel or aircraft, to stop the vessel, and with instructions to facilitate safe boarding and inspection for the purpose of enforcing any applicable Canadian fisheries law, the Agreement, or this subpart. All of the provisions of § 300.5 regarding communications, boarding, and signals apply to this subpart. For purposes of this subpart, authorized officer in § 305 means an authorized officer of the United States or Canada. (See paragraph (b) of this section for specific requirements for complying with signals and instructions issued by an authorized officer of Canada.)(b)Canadian signals. In addition to signals set forth in § 300.5 , persons aboard fishing vessels subject to this subpart must immediately comply with the following signals by an authorized officer of Canada. (1) Authorized officers of Canada use the following signals to require fishing vessels to stop or heave to: (i) The hoisting of a rectangular flag, known as the International Code Flag "L", which is divided vertically and horizontally into quarters and colored so that: (A) The upper quarter next to the staff and the lower quarter next to the fly are yellow; and(B) The lower quarter next to the staff and the upper quarter next to the fly are black;(ii) The flashing of a light to indicate the International Morse Code letter "L", consisting of one short flash, followed by one long flash, followed by two short flashes (. - . .); or(iii) The sounding of a horn or whistle to indicate the International Morse Code letter "L", consisting of one short blast, followed by one long blast, followed by two short blasts (. - . .).(2) Authorized officers of Canada use the following signals to require a fishing vessel to prepare to be boarded:(i) The hoisting of flags representing the International Code Flag "SQ3"; or(ii) The flashing of a light, or the sounding of a horn or whistle, to indicate the International Morse Code Signal "SQ3" (. . . - - . - . . . - -).