Ciao --- Meaning

I read it in a book .. so not sure how much true it is, but it says:
It's an abbreviation of a phrase used in medieval Venetians as an intimate salutation: Sono il suo schiavo! Meaning: "I am your slave!"

Ha ha ... I can't believe it really means that .. we all use it so often and I am still doubtful. Can someone do a check on this ? I am sure Girish will :-)...

Let me know if you know!

~Krupa