You're probably wondering what exactly a "sister's sausage" is as well as why it's pink and why the name sounds vaguely euphemistic. So does every kid who grows up in Finland but sadly, the truth behind the name is not as interesting as you might think- from the wikipedia entry on siskonmakkara:

The word siskonmakkara is a partial loan translation from the Swedish compound word siskonkorv (korv meaning "sausage") whose siskon part had originally been susiskon, derived from German Sausischen and French saucisse, both meaning "small sausage". The word siskon is a homonym of the genitive form of the word sisko meaning "sister", as the word siskonmakkara appears to mean "sister’s sausage".