The combination on the lock that Mary used was 1-24-79: Dean's birthday. Also this episode aired on January 24th, which is Dean Winchester's 40th birthday.
When Mary looks in on Dean, he is in his favorite sleeping position, the "Marty McFly" position right arm behind his back, face down into the pillow as in the Back to the Future (1985) movies.
In the United Kingdom, Satan is also known as "Old Nick." Nick was the vessel of Lucifer, or the Light Bearer.