"Zwo" ist not really a military code, it is very often used in everyday german language. It is used because the real word, "Zwei" (2) , sounds very similar to "Drei" (3). So in situations where it is important to understand the number, you will use "Zwo".

-"My phone number is 84328" would be:
"Meine Telefonnummer ist Acht, Vier, Drei, Zwo, Acht."

But it is not the "Zwo" that is interesting, but the word "Links".
He sings "Sie woll´n mein Herz am rechten Fleck", which can also be translated to "They call me a fascist", since "Rechts" also means conservative or fascist. So, when he says that his heart beats "Links", he means that he is not a Nazi, like many people say, but a socialist. It is a very controverse song, since the music does not sound like a socialist song, but rather like a Neonazi song.