I thought that S=single in the beginning too, but that would mean the whole ship of singles. I think there are families involved on this voyage too, parents and children.
I don't know, what is the connection with Trieste. As I said, this list was written down in Croatian. I found the list of Bet Aliyah ships. Ships to Palestine were leaving from Bakar, small port near Rijeka, both in Croatia. Don't you know the name of the ship? Is this A. Hitzky your relative?
My suggestion is to go on Israeli forum here on genforum. Maybe there is someone who is familiar with history of immigration shortly after WWII. IF this really is a list of passengers on ship going to Palestine.