I hate to stir the pot, but I'm voting "Yo, Bro." That silly mark is a comma that got a sip of the Fizzy Lifting Drink.
The designers are the final word in my book. On the title screen, it's obviously "Yo, Bro." Though it's a stupid name, the comma's not incorrect. "Yo apostrophe" means nothing. True, "Yo' Bro" does appear in more places, but it was likely some marketing goob that misread the mark, transcribed Yo apostrophe Bro and f*cked it all up.
True story: there's a Depeche Mode b-side named Stjarna (Swedish word for star I think?) which was known by fans forever as St. Jarna. Many years after the fact, it became known that as the single (Little 15) was going into production, someone at the record company misread the word and put down St. Jarna as the name. All the singles were pressed that way, and even when they re-released them years later they still read "St. Jarna." Most true fans like myself know it now as it was originally intended by the songwriter: Stjarna.
Moral of the story: Yo, bro, like it or not it's "Yo, Bro."
Therefore, the correct way to say it is "Yo, Bro," as in: "Yo, bro, pass me the controller; it is my turn to play in this two-player game of Yo, Bro."
Quote edited for spelling, punctuation, grammar and factual inaccuracies.