The Register - The Mexican archaeology institute says that a second possible reference has been found to a date in December 2012 as the end of a 5,200-year Mayan calendar cycle after which "the cosmos is regenerated". Reportedly the glyph in question is carved into the back of a brick found in ancient temple ruins - suggesting that it was a hidden secret, not meant to be seen.
The Tortuguero glyph is well known, and is the source of much of the hoopla regarding the Mayan calendar and possible doomsday in 2012. The Comalcalco glyph, probably inscribed in the 7th century AD, is less commonly known and many experts doubt that it refers to December 2012 at all: it might refer to the same point in a different 394-year-long "Baktun" during the present 5,200-year long count.
Intriguingly, however, the AP reports that the Comalcalco brick shows signs that its cryptic glyphs were actually on the inside or covered in stucco, so hidden from view while the temple of which it was part still stood.
The Mexican archaeological institute seeks to downplay the significance of the expiration of the thirteenth and final Baktun of the current long count on or about December 21 next year....Similarly US space agency NASA has issued several rather equivocal denials that there's any truth to the 2012 apocalypse theories, saying that while mega solar flares and/or colossal "super volcanoes" most likely won't destroy the entire Earth, they could certainly cause titanic disasters and suffering on an immense scale.