What is the meaning of the word "sign"?

Definitions:

a character indicating a relation between quantities noun
- don't forget the minus sign
a fundamental linguistic unit linking a signifier to that which is signified noun
- The bond between the signifier and the signified is arbitraryde Saussure
a perceptible indication of something not immediately apparent, as a visible clue that something has happened noun
- We showed signs of strain after over 30 hours in transit.
a public display of a message noun
- I posted signs in all the shop windows.
any nonverbal action or gesture that encodes a message noun
- signals from the boat suddenly stopped
any objective evidence of the presence of a disorder or disease noun
- There were no signs of asphyxiation.
be engaged by a written agreement verb
- Our band signed to play three shows this month.
communicate in sign language verb
- I don't know how to sign, so I could not communicate with my deaf cousin
communicate silently and non-verbally by signals or signs verb
- They signed their disapproval with a dismissive hand gesture.
engage by written agreement verb
- They signed two new pitchers for the next season
place signs, as along a road verb
- sign an intersection
structure displaying a board on which advertisements can be posted noun
- the highway was lined with signboards