Postal Code for earth

Should you be happening to be in Alpha Centuri posting home a postcard it may well be a mistake to post a letter to Earth.

After all there must be some hierarchy such as the name of the solar system and then the number of the planet away from the local star.

So it would be better to post your cards to 'Sol-3' (local name:Earth). After all that is how they seem to name planets in tv shows like star trek so why isn't earth known as Sol-3.