A resemblance between the external character of a disease and those of some physical agent, for instance, that existing between the red skin of scarlet fever and a red cloth; supposed to indicate this agent in the treatment of the disease.
Text (or images, etc.) appended to a user's emails, newsgroup posts, forum posts, etc. as a way of adding a personal touch. Email signatures often include extended contact information. Forum signatures often serve as a way for a user to express themselves (song lyrics, art, etc.).