I’m on vacation for a week, and I celebrated by watching the San Francisco Giants host the Oakland Athletics in their first interleague games of 
the season.
I wish I had one of those A’s-Giants combo caps that were available during the 1989 Bay Bridge World Series, the one that was interrupted by the Loma Prieta Earthquake. A good friend back east still has his, but I can’t even find a photo of one. This ersatz Giants’ cap in the A’s green and gold will have to do.
The San Francisco Bay area is the only market where a twin logo cap could exist. In New York, would any fan of either the Yankees or Mets want to share space on the crown with the other team’s NY? No way.
In Chicago, would a Cubs or Sox fan tolerate such? Never.
In LA? Angels and Dodgers together? Inconceivable.
Around San Francisco Bay, fans have fierce allegiance to their team, but it’s a market that appreciates both franchises. I take the twin logo cap as a signal that Bay Area people are true fans of the game, recognizing the value of both the American and National leagues.
(The Giants won tonight on a 3-0 shutout by Tim Lincecum. I was rooting for the Giants.)
The Ball Caps Blog 
Definitely not in Chicago.
I have one of the giants oakland caps. I was trying to find out it’s value when I found your website. It’s for sale if your interested
I still have the giants / a’s ball cap. If anyone is interested in it. mikemartin6163@yahoo.com