Natural Signamancy refers to the appearance of units, with some implication that the exterior appearance is tied to an interior predisposition or personality.
Jillian: Became queen and began to lose some of her lean warrior muscle appearance. Looked fuller and more "royal."
Slately: Claimed that signamancy was a terrible curse. It revealed his true nature, "No unipegataur-riding warrior king was he, no towering leader and orator." Since he avoids battle and allows his chief warlord and other princes run the kingdom for him, he has shrunk, gotten fat, and his hair has turned white.
Also, other leaders appearance reflect a less vigorous lifestyle and may be due to signamancy. Don King and Al Frappacino. What effect if any it might have on Stanley (a non-Noble Infantry Unit promoted up through the ranks to Overlord) are unknown, but his stature seems the same as in flashbacks and he is known to still engage in combat on occasion (such as taming dwagons).
- Caster abilities: As of yet Unknown
As of yet, no known Signamancer has been introduced, but apparently Transylvito has some.
Hippiemancy is the magic of relationships: detecting and altering the forces of opposition and attraction which bind people or units. 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. Author and creator 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.
As Signamancy supposedly deals with the relation of what is seen and what is there it's likely that Signamancers are at least good at psychology if it's not actually included in the abilities.
Signmancy may have to do with refusing the intangible rules, as in a protest with signs where units seeing it are caused to have to 'roll against loyalty/duty' and on a fail be able to disobey orders without popping out of existence.
Real World References
Also, analogous to Enlightenment/Awakening in general  particularly in light of Signamancy being an discipline of Hippiemancy with a sister discipline of Flower Power. For example that "The Signamancers claimed that all Stuff was Foolamancy." Erf-b1.5-p037 (note capitalized "Stuff" and "Foolamancy") is perhaps a paraphrasing directly the phrase "the world is illusion" as it is often expressed from an Enlightened perspective.