Those who know chemistry know that gold is aurum. And its short name in periodic table is Au. That`s from the scientific point of view.
On the other hand, in Russian language we have a separate word “au”, which is actually “hey!” or “hello!” in English, and when someone gets lost he is shouting “au” so that other people could hear, or when you can`t find someone or hear something, you also say “au”.
So here we play on both meanings, using slogan Gold is calling (Aurum is calling “au”)