Definitions of sign:

• noun:   a perceptible indication of something not immediately apparent (as a visible clue that something has happened)

  Example: "He showed signs of strain"

• noun:   a public display of a (usually written) message

  Example: "He posted signs in all the shop windows"

• noun:   a character indicating a relation between quantities

  Example: "Don't forget the minus sign"

• noun:   a gesture that is part of a sign language
• noun:   a fundamental linguistic unit linking a signifier to that which is signified

  Example: "The bond between the signifier and the signified is arbitrary--de Saussure"

• noun:   (medicine) any objective evidence of the presence of a disorder or disease

  Example: "There were no signs of asphixiation"

• noun:   structure displaying a board on which advertisements can be posted

  Example: "The highway was lined with signboards"

• noun:   an event that is experienced as indicating important things to come

  Example: "It was a sign from God"

• noun:   having an indicated pole (as the distinction between positive and negative electric charges)

  Example: "Charges of opposite sign"

• noun:   any communication that encodes a message

  Example: "Signals from the boat suddenly stopped"

• noun:   (astrology) one of 12 equal areas into which the zodiac is divided
• verb:   engage by written agreement

  Example: "They signed two new pitchers for the next season"

• verb:   approve and express assent, responsibility, or obligation

  Example: "Have you signed your contract yet?"

• verb:   be engaged by a written agreement

  Example: "He signed to play the casino on Dec. 18"

• verb:   communicate in sign language

  Example: "I don't know how to sign, so I could not communicate with my deaf cousin"

• verb:   mark with one's signature; write one's name (on)

  Example: "She signed the letter and sent it off"

• verb:   communicate silently and non-verbally by signals or signs

  Example: "He signed his disapproval with a dismissive hand gesture"

• verb:   place signs, as along a road

  Example: "Sign an intersection"

• verb:   make the sign of the cross over someone in order to call on God for protection; consecrate