Sigil damage thrusts player toward the east
In Strife, the Sigil weapon is powered by the player's own life force, and therefore when the Sigil is fired, the player loses an amount of health that is proportionate to the number of Sigil pieces he has acquired.
When this damage is done to the player by code in the Sigil's firing action function (named A_FireSigil in Chocolate Strife), the player is passed as both the target and the inflictor. The Doom engine will always inflict thrust when an inflictor is involved in damaging another object. However, in this case, since the target and inflictor are the same object, the function R_PointToAngle2 always returns an angle of 0 degrees, or straight to the east in Doom's coordinate system.
This means that no matter what direction the player is facing when the Sigil is fired, he will be thrust toward the east. This can be quite counter-intuitive, since a large and powerful weapon like the Sigil would be expected to cause a consistent kickback effect instead.