By saying “signs like this,” Jesus means that the signs and marvels He mentioned above are only a few of the signs He will work to accompany our proclamation of the gospel. There are many other ways that Jesus backs up those who spread His word.
When Jesus backs up our evangelization, we call this a “confirmation” of the word we have shared. “The Lord [continues] to work with” us as we witness to Him “and confirm the message through the signs” He chooses (Mk 16:20). A sales representative would be delighted if the president of her company confirmed her sales presentations to her clients. We who witness for Jesus have an even greater marketing confirmation service. Think of it! “The God of all grace...will Himself...confirm” us as we witness to Him (1 Pt 5:10).
The Lord is the same today as yesterday (Heb 13:8). As He has backed up St. Mark’s preaching, so He will confirm our evangelization and preaching in the hearts of our listeners. If signs and confirmations of the Gospel are not commonplace today, one possible reason may be that we aren’t spreading the gospel as the Lord wants us to. He will back us up. Therefore, “go into the whole world and proclaim the good news to all creation” (Mk 16:15).