Ave, Allies.
Our belief system of Creeperism has long since been without substance since the upheaval and destruction of the Library and a significant portion of the records across the Empire. Indeed, any of our mutli faceted and varied beliefs are lacking in any substance and form at this point in time.
CreeperismThe belief that the Great Creeper is omnipotent, omniscient, and that It's Servants, the mottled green skinned quadrupeds that we see across the lands of the Empire today. These are the eyes and ears of the Great One. The belief that each Creeper is Sacred, and also sent down to the world to Test each of us. Their presence reminds the faithful to always be vigilant, and to always be aware.
Notable Examples Creeperism, as I recall it, has long since been the belief of the Valyrian Realm. Going back far into the mists of time, the belief in the Great Creeper has been the mainstay of, in particular, the Kingdom of Valtoros, and its people.
King Kyn is an example of the most devout believer, with a back-spanning tattoo of the symbol of belief
King Kyn's tattoo
And the Royal Crest of Valtoros.

As the legends go, the previous King of Valtoros was on a quest to find one of the High Servants of the Creeper, the mythical Golden Creeper. His death shortly thereafter allowed him to die with peace of mind. Records show that there was a painting done to commemorate the event, but time will tell if it can be found again.
More input from the Valyrians is welcome on this subject.