Here's a trailer that is mildly spoilery for the special, using Mark's text (in second Tweet).
Dearest @Markgatiss STOP Your telegram to Dr Watson has arrived STOP #Telegram221B pic.twitter.com/8qWYIdeeB5— Sherlock (@Sherlock221B) December 16, 2015
My dear Watson. Stop. See you on the television and the kinema on New Year’s Day! Stop. Please don’t ever. Stop. #Telegram221b— Mark Gatiss (@Markgatiss) December 16, 2015
By the bye, Radio Times has a LOT of articles -- like Did you spot these clues and references in the new Sherlock trailer? -- and Martin Freeman has the best quote yet in new Sherlock teaser...
Now to shift into present day, with other members of Team Sherlock: i.e, Cuffs -- and the Marvel Universe.
Should #Cuffs have been cancelled? Have your say! https://t.co/ERqAuU4Ckm @eleanormatsuura @CHIMPSINSOCKS pic.twitter.com/4VlKVxbVW0— Radio Times (@RadioTimes) December 17, 2015
(The Cuffs link to Radio Times here also, and the Marvel link as well.)
#MartinFreeman's character is in MORE #Marvel films after #CaptainAmericaCivilWar! https://t.co/PHyXArUtdw pic.twitter.com/IDm6ry5HxC— Radio Times (@RadioTimes) December 4, 2015