bummer- no pun intended. It's the only drawback of a Brooks saddle they're a thief magnet on a commuter bike.
My Brooks got smashed while locked to a parking meter when a delivery truck backed onto my bike. It was the only thing on my bike that looked like it had any value. I also had a cylcometer ripped off too- just the display unit- they left all the other parts on the bike. I don't leave anything on the bike nowadays except for my milkcrate, which makes the bike look particularly unattractive.