There is a difference between seeking direction and desiring a sign as proof before believing. Probably one of the most noted individuals who sought a sign for direction was Gideon. Gideon sought a sign out of cautiousness and not unbelief. Had that not been the case, he would have been rebuke by the Lord.
An adulterous generation seeks a sign because their heart has affinity to another. Their request for a sign is more out of not wanting to change than it is for desiring the truth. Their prideful heart digs in becoming unmovable.
This attitude is understandable for the lost, but the saddest of testimonies for the saved.