This chart powerfully demonstrates the connection between the preaching of the gospel and the signs, miracles, and wonders which followed as confirmation of that first century message.
Jesus promised his disciples that in order to confirm the gospel, “signs” would follow those who believe. However, the gospel which Jesus and his disciples preached was the good news of the soon-coming kingdom which would be established within their generation. Therefore, the “signs” confirmed their message that the kingdom of God would be received by the first century generation. Since the gospel was received in AD70, there is no need for signs to confirm the coming of a kingdom which has already come. This explains why we don’t see “confirming signs” today.