IATA airline designator
IATA airline designators, are two-character codes assigned by the International Air Transport Association (IATA) to the world's airlines in accordance with the provisions of IATA Resolution 762. They form the first two characters of the flight number Designators are used to identify an airline for all commercial purposes, including reservations, timetables, tickets, tariffs, air waybills, and in airline interline telecommunications.

ICAO airline designator
The ICAO airline designator is a code assigned by the International Civil Aviation Organization (ICAO) to aircraft operating agencies, aeronautical authorities, and services. The codes are unique by airline contrary to the IATA airline designator codes.

Call signs
Most airlines employ a distinctive and internationally recognized call sign that is normally spoken during radio transmissions as a prefix to the flight number.
Some call signs are less obviously associated with a particular airline than others. This might be for historic reasons, or possibly to avoid confusion with a call sign used by an established airline.

Aircraft Tail Prefix
In accordance with the Convention on International Civil Aviation all aircraft must be registered with a national authority. Because airplanes typically display their registration numbers on the aft fuselage just forward of the tail, in earlier times more often on the tail itself, the registration is often referred to as the "tail number”. The prefix of the tail number is country specific in many cases a combination of both country and applicably specific.

ICAO Aircraft Type Designators with Wake Category used to classify aircraft types that are most commonly provided with air traffic services.
Wake Category
 L Light
M Medium
 H Heavy

For more information please download the following document. Click here: ICAO Aircraft Codes Explanation