Tell me, have you
seen the Yellow Sign?
A
symbol of the
power of
Hastur. It looks like a
harmless yellow squiggle, but it appears to
squirm when you
look at it for a while, and it holds the power to
warp dreams. Its
appearance often
heralds the coming of
the King in Yellow. Most of its exposure has come from the stories of
Robert W. Chambers and the
Call of Cthulhu roleplaying game.
"The Yellow Sign" by Robert W. Chambers (see Cletus' node below)
Encyclopedia Cthulhiana by Daniel Harms, p. 236