Preached Everywhere

Mark 16:19-20   
19 So then, after the Lord had spoken to them, He was received up into heaven, and sat down at the right hand of God. 20 And they went out and preached everywhere, the Lord working with them and confirming the word through the accompanying signs. Amen.

When Jesus left for heaven after coming back from death and instructing His followers further, He told them as apostles they would be able to do some of the same miraculous things to prove, to confirm that they were with him and spoke on His authority. It was not about the signs, but who these pointed to.  As we see in Acts, without these proofs the gospel would be uncertain and he epistles written not accepted by these men.  So Jesus was seen in them and the prophetic word more certain by His word has come to us now.
(2 Peter 1:19) And so we have the prophetic word confirmed, which you do well to heed as a light that shines in a dark place, until the day dawns and the morning star rises in your hearts;