Thinking about the shape of the Doom symbol. The one in this poster is not like the red and black symbol shown during the credits. But contrary to memory, there is no single standard; there are many variant symbols in the movie.
A - Battle standard. There is a variant of this one with bells and hair (scalps?).
B - Thulsa Doom wears a snake amulet on an elaborate chain; the amulet looks very similar to the one worn by the princess, but they are different.
C - The symbol above Doom's nook in the Mountain of Power.
D - Rexor's leather armor worn during the raid has a double snake motif sewn onto it.
E - Rexor wears an amulet unlike Doom's other priests during the Tower of Set scene. In later scenes, he wears the other kind (H - presumably because this one got caught in his hair/face during the action?)
F - The symbol on Rexor's headpiece is the same shape as Doom's.
G - Guards at the Mountain of Power have a unique symbol on their breastplates and shields.
H - Priests and servants of Doom wear an amulet like this one.
I - The jade amulet found in the Tower of Set.
J - The princess wears a unique amulet.
A - Symbol shown when the credits roll. This exact symbol is never seen in the movie.
B - Thulsa Doom's shield. Close to A but not exact.
C - Shields and tridents of Doom's guards bear different snake symbols.
D-H - Production drawings.
If you watch closely, there are many more variations in the movie. But most of them have either the shape of a W (or lower-case Omega) or an O. I might adjust the poster to better imitate shield B or D.
