Actually ... there is a really strong legal precedent against trademarking "Winter is Coming." There was a Linux company named "Lindows" at one point, and Microsoft challenged the company, saying the name was too close to "Windows." Lindows argued that you can't trademark a common name like "Windows." Microsoft finally settled with them out of court, and gave them something like $100 million to change their name to "Linspire."
So that painting may be worth $100 million. It's very nice!