re: Crackpot ASOIAF Theories SPOILERS

Compare the Pink Letter with all the other letters that Ramsay wrote

Letter to Asha about Moat Cailin being taken
It was tightly rolled and sealed with a button of hard pink wax.
A scrap of leather fluttered down into her lap. When she read the dry brown words, her black mood grew blacker still
“Ramsay Bolton, Lord of Winterfell, he signs himself.
Those were done in maester’s ink, made of soot and coal tar, but the message above was scrawled in brown in a huge, spiky hand.
“I write this letter in the blood of ironmen,” the last, “I send you each a piece of prince. Linger in my lands, and share his fate.”

Letter to Jon about Moat Cailin
It was tightly rolled and sealed, with a button of hard pink wax.
Ramsay Bolton, Lord of the Hornwood, it read, in a huge, spiky hand. The brown ink came away in flakes

Unfortunately, we don't get a description of the Pink Letter, besides the smear of pink wax. The previous letter to Jon and the letter to Asha has a button of hard pink wax. There's no mention of how Ramsay addresses the letter to Jon in the previous letter, but the Pink Letter he just says "bastard." Also, he writes the other letters in blood, and has a spiky hand. I wish there was mention of the ink and handwriting in the Pink Letter.

Then there's the use of bastard. Ramsay doesn't let anyone use the term bastard in his presence, but I'm not sure if that would rule out that Ramsay would call him that.

Then there's Mance using the term bastard. In Storm, when he's disguised as Rattleshirt:
“Not me. I’m done with those bloody fools.” Rattleshirt tapped the ruby on his wrist. “Ask your red witch, bastard.”
“I’ll range for you, bastard,” Rattleshirt declared.

Remember that Jon's excuse for joining the wildlings is because he's bastard. I think Mance was mocking him, and was angry at being betrayed. Although later on, Mance starts calling him Snow or Lord Snow (I'll have to double check if he calls him bastard later on).

And how in the world would Ramsay know it's Mance? Everyone thinks he dead. Even if Mance were being tortured, I doubt he'd reveal that info. All he'd have to say is that he's some random guy that Jon sends to save "Arya." I think he did it in order to provoke Jon into going south. I don't think he could have known that Marsh and co. would be dumb enough to murder Jon in front of all the wildlings and other NW members. Of course, there may be more to it than just that, but that's getting into the whole Northern Conspiracy stuff (Mance's involvement is a bit more crackpot though).