INTERPOL’s communications system facilitates three kinds of messages.

1. Simple messages between one or more NCBs. Basically, this is your everyday email and it is not necessarily seen by INTERPOL unless specifically included.
2. Diffusions – A more structured email that can be sent to one or more NCBs addressing a wide variety of concerns including identifying someone as a suspect or requesting a person’s arrest. Diffusions are not subject to prior review by INTERPOL but the agency is automatically copied and may review the diffusion for compliance after the fact.
3. Colored Notices – Any NCB can request the publication of a notice, but all requests are subject to review by INTERPOL for administrative compliance with its rules before publication. By rule, all notices must be published to all INTERPOL member nations.
   • Yellow Notices: To alert police to a missing person.
   • Blue Notices: To collect additional information about a person in relation to a crime.
   • Green Notices: To provide warnings about persons who have committed criminal offenses and are likely to repeat those offenses in other countries
   • Red Notices: To “seek the location and arrest of wanted persons with a view to extradition or similar lawful action.”

Yellow, blue and green notices are all relatively common, but by far the most-used notice is the Red Notice, of which 13,048 were published in 2017.