The term translated “signs” is the word commonly used in the New Testament for miracles. Almighty God has all things so fully in his hands that not a bird falls to the ground without his will (Matthew 10:29). Commonly he directs the events of his world according to set patterns. The term “signs” is generally used to describe those times when the Lord directs events in an uncommon manner (e.g., making water stand in a heap, filling the land with frogs, making the sun stand still, feeding crowds with a few loaves of bread). The purpose of his signs is to demonstrate the validity and reliability of his Word. As people are finite, people do not have the power to perform miracles on their own strength; God needs to work through them, as he did, for example, through Moses with the plagues of Egypt.
Being a creature, Satan is also finite, as are also his angels (demons). Being the deceiver (Revelation 12:9; John 8:44), he seeks not only to deceive people through his words (recall the “mouth” of Revelation 16:13) but also to copy God’s miracles in an effort to persuade people that his words are valid and reliable (Exodus 7:11, Exodus 7:22; Exodus 8:7). The second beast of Revelation 13 had also performed great signs (Revelation 13:13).
14 For they are demonic spirits, performing signs, who go abroad to the kings of the whole world, to assemble them for battle on the great day of God the Almighty.