Signs are the language of God, angels, and prophets. Their purpose may be to communicate the approbation of heaven, as in the promise that signs will follow them that believe (D&C 84:65-73; Mark 16:17-18), or to dramatize divine displeasure, as with the plagues of Egypt (Exodus 4:8 ff).
In the scriptural sense, a “sign” is something by which another thing is shown or represented, and this often in a miraculous manner. Numerous words share a close kinship with it and thus constitute commentary on its meaning. They include signal, signature, signify, and ensign. Companion words include token, mark, and wonder. Signs and wonders are a word-combination that appear frequently in the scriptures.