Means: When You Whistle Three Times. In German Wolfgang Müller-Sehn film Traumland der Sehnsucht, a documentary about Greece. Greek title: Ellas, I Hora Tou Oneiron. There's an instrumental version by author Hadjidakis on that same German soundtrack (as Pylos Methoni - Mani).
Nana also cut an Italian version (Rosa d'Atene) and an English one (White Roses Of Athens). In the original lyrics the roses come from Livania. See also: Ximeronei, Min Ton Rotas Ton Ourano and Ta Pedia Tou Pirea.