According to Spike Lee, from his Bad 25 documentary, "Shamone" "isn't just a cool way to say "come on," but MJ's tribute to soul singer Mavis Staples, who used it in a live version of "I'll Take You There" in 1975."
Shamone comes from the Michael Jackson song "Bad" released in 1987. It is a distinctive deliberate mispronunciation of "come on" used frequently by Jackson, occasionally spelt "cha'mone", "jamone" or more commonly "shamone".
Today shamone can be used pretty much the same way "word" is commonly used.
"Come on, man, we're going to the bar. I said, SHAMONE!"