English dictionary definition of:

sign

structure displaying a board on which advertisements can be posted
a perceptible indication of something not immediately apparent (as a visible clue that something has happened)
any nonverbal action or gesture that encodes a message
a public display of a message
a character indicating a relation between quantities
a gesture that is part of a sign language
a fundamental linguistic unit linking a signifier to that which is signified
an event that is experienced as indicating important things to come
(astrology) one of 12 equal areas into which the zodiac is divided
having an indicated pole (as the distinction between positive and negative electric charges)
(medicine) any objective evidence of the presence of a disorder or disease

make the sign of the cross over someone in order to call on God for protection; consecrate
be engaged by a written agreement
communicate in sign language
mark with one's signature; write one's name (on)
communicate silently and non-verbally by signals or signs
place signs, as along a road
engage by written agreement
approve and express assent, responsibility, or obligation