While I don't particularly like the Giants, I must say I do like what San Francisco brings to baseball. San Francisco has always been one of the United States' more eccentric cities, as well as one of its more progressive ones. Its countercultural history has informed its identity, and this identity is expressed in its attitude toward baseball. The Panda hats, the Brian Wilson beards (primarily worn by ladies, it seems); these are things that make sense on the heads of San Francisco baseball fans. Of course, these accessories relate to actual Giants players, players who are also somewhat unique and eccentric in a manner fitting of their city: the Panda, Pablo Sandoval, a very large and exuberant man widely beloved in San Francisco; and closer Brian Wilson, with his beard more impressive than any replica any fan could wear, his jersey undone several buttons to show off his chest hair. Tim Lincecum also deserves mention here; his surfer hair and violent delivery absolutely belong in San Francisco.
There are also things like the World Championship Baby promotion the Giants are currently running: expecting Giants fans are encouraged to enter a contest which would award the first baby born after 7:54 p.m. on August 1 (the moment exactly 9 months after the Giants got the final out to win the 2010 World Series) the title of "World Championship Baby."
Of course, also making the baseball scene in San Francisco easy to love are the facts that it's home to one of baseball's most beautiful ballparks, and that the Giants sell out this ballpark almost every night. The atmosphere at AT&T park is fantastic, and games there are a joy to watch (although I do find their broadcasters a bit annoying).