- As of yet Unknown
As of yet, no known Signamancer has been introduced, but apparently Transylvito has some.
While no actual Signamancers or Signamancy has appeared in Erfworld canon yet, we can infer some things about the discipline's nature from indirect comments on it. Rob Balder has said about Signamancy, "Signamancy. Like the Peace sign, man. Like the protest sign, man. Signs, signs, everywhere a sign. Far out." The precise meaning of this is unclear; however, he is drawing a direct link between a visible symbol or word and a desired result. This is further strengthened by the nature of Signamantic philosophy - that all physical appearances are simply symbolic manifestations of the underlying "truth" of Erfworld.Erf-b1.5-p037 Based on these, it seems that Signamancy is in some way concerned with the relationship between "real" things and the symbols that represent them - the relationship between the map and the territory, so to speak. Signamancy is also a Hippiemancy, which may indicate certain things about the flavor and details of the discipline, but since no other Hippiemancy is adequately described as of now, it is hard to draw concrete conclusions from this connection.
It has been speculated that Parson Gotti (AKA Lord Hamster) is a Signamancer (based on Signamancy being Fate-aligned and Janis's claim that he is a Hippiemancer of some sort). Parson has created in Gobwin Knob a set of street signs based on characters from the Simpson's and his favorite foods. If Parson is a Signamacer, then these signs may begin to effect the streets on which they are located.
Real World References
The Signamantic philosophy is highly reminiscent of Plato's philosophy, espoused in the Allegory of the Cave, in which Plato explains how perceived reality is nothing more than the shadows of the true reality.