The saving icon in the game changes on certain days to remember several fallen pioneers in heavy metal music.
On February 19th the saving symbol changes to a lighting bolt. A reference to former AC/DC vocalist Bon Scott who died on said date.
The same also applies to Randy Rhoads (former guitarist for Ozzy Osbourne) and "Dimebag" Darrel (guitarist for both Pantera and Damageplan) where on March 19th and December 8th, both dates on which the respective musician died, the saving symbol changes to a "PR" and a dime respectively.