This guy has been seen riding a penny-farthing, also known as a high-wheeler bicycle, in the bike lane down Market Street, and SF Weekly immediately called the SFPD on him to see if he was breaking any laws.
According to media-relations Officer Albie Esparza, this is, indeed, perfectly legal, and he's seen the guy riding around SoMa too. Goofy as it is, it is just a bicycle.
As friend of SFist Joe Herman puts it, posting his own photo, "Seriously, where else in the world would you see someone legitimately and non-ironically using [one of these] to commute." Yes... Only In SF. (And Portland.)