= SAMO started as an inside joke when
Jean-Michel Basquiat and a few of his friends were still teenagers, they tagged funny/thought-provoking lines all over NYC (especially SoHo) in the 70s.  sometimes they were plays on words.. everyone was tryin to figure out who the hell was behind them. 

they were smokin pot talkin about how everything is just the 'Same ol shit..

An abbreviation for the city of Santa Monica, CA, as well as Santa Monica High School. " Samohi" is more commonly referenced to Santa Monica High School, while "Samo" is a more popular reference to the city. 

"Can we meet in Samo tonight?" 
"Don't say Santa Monica.  To many syllables.  We refer to it as Samo"