The deal: $2 Cold Cut or Meatball Marinara 6 inch subs. Starts today Nov 27th thru Dec 31st. No coupon required, YMMV depending on individual location.
I've posted this every year Subway does it during December since 2011. Just got another flier in the mail today. I think they skipped December 2016, but happy to see its back for Dec 2017. It's the best deal they do all year, provided you're ok with those types of subs. From my experience the employees are cool about letting you order a cold cut without the meat if you just want the veggies on it.
Here's the thread from 2012 talking about individual experiences https://slickdeals.net/e/5595586-subway-2-subs-december-s-customer-appreciation-month-ymmv