Found 17th Jan 2012
For the past 2 years I've received a free cookie from subway on my birthday. They send an email to you with the voucher, or you can just use your subcard and they scan it in to redeem. It's a QR code IIRC. It expires around a month after your birthday, but it's free! It's saved me from starvation once, hope it does the same for you!