Franz Ferdinand is growing awfully fond of “secret” shows. The band’s New York gigs never stay secret for long, however, and such was the case with a quickly sold-out showcase at Brooklyn’s Music Hall of Williamsburg on October 8th. Consider it a gift to the tri-state area’s fan base, which filled the 550-capacity Music Hall to hear a mix of old favorites and new tunes from Franz’s upcoming third LP, Tonight. The crowd mainly consisted of older folks who didn’t let a little thing like maturity get in the way of rocking out to Franz Ferdinand, a band that has treated New York City like its second home in recent years.