IATAN stands for the International Association of Travel Agents Network. They are an industry association designed to represent the interests of their member companies.
In addition, they (along with the IATA) are the body responsible for the standard international codes for airlines, airports, hotels, cities, and car rental firms (for example, the three-digit codes that designate London Heathrow Airport as LHR).
Its main goal is to assist travel agents to meet and maintain a specific set of standards that are of value to airlines, the agency community, as well as to consumers.
IATAN then executes an Agency Agreement between the agent and the airline which gives the agent the legal right to ticket on that carrier.
When the IATAN logo is displayed in a travel agency's window, on business stationery and press releases, it demonstrates the agency owner's connection with the international travel community.