Signs are given to confirm God's word. They may warn the rebellious or encourage the faithful. People may seek signs as a result of a genuine desire to serve God.
Signs are given to demonstrate God's power
See also
pp Ps 105:4-5
Signs demonstrate the authority of God's servants
Moses and Aaron
Elijah
Elisha
Jesus Christ
The apostles
Signs may accompany the preaching of the gospel
Signs may warn the ungodly of impending judgment
The prophets often acted out their messages for greater effect:
Signs may warn God's people against rebellion
Signs may encourage faith
By giving guidance
pp 1Ch 14:14-15
By giving assurance of God's presence
By encouraging the fearful and doubting
pp 2Ki 20:8-11
pp 2Ch 32:24
Signs need hold no terror for the godly
pp Mk 13:7
pp Lk 21:9
Seeking signs
When seeking signs is acceptable to God
When seeking signs is condemnned by God
pp Mk 8:11-12
pp Lk 11:29