Complex sentence: Listeners were allowed to join the MFA too; if you joined you got a letter, an ID card and a "Whammy Cloth;" a handkerchief-sized piece of material emblazoned with his name and the logo of the radio station.
Split into simpler sentences: Listeners were allowed to join the MFA too; if you joined you got a letter, an ID card and a "Whammy Cloth". Which was basically this handkerchief-sized piece of cloth emblazoned with his name and the logo of the radio station.