Noun

1. A perceptible indication of something not immediately apparent (as a visible clue that something has happened)
2. A public display of a message
3. Any nonverbal action or gesture that encodes a message
4. Structure displaying a board on which advertisements can be posted
5. (astrology) one of 12 equal areas into which the zodiac is divided
6. (medicine) any objective evidence of the presence of a disorder or disease
7. Having an indicated pole (as the distinction between positive and negative electric charges)
8. An event that is experienced as indicating important things to come
9. A gesture that is part of a sign language
10. A fundamental linguistic unit linking a signifier to that which is signified; --de saussure
11. A character indicating a relation between quantities

Verb

1. Mark with one's signature; write one's name (on)
2. Approve and express assent, responsibility, or obligation
3. Be engaged by a written agreement
4. Engage by written agreement
5. Communicate silently and non-verbally by signals or signs
6. Place signs, as along a road
7. Communicate in sign language
8. Make the sign of the cross over someone in order to call on god for protection; consecrate