I am sure there are Charismatics that believe that tongues are a sign of salvation, but most that I am acquainted don't believe it is. They would say that tongues are the second blessing associated with the baptism of the Holy Spirit.
In other words they believe that it is the power to live a Christian life in areas like witnessing.
While I was a Pentecostal years ago, my old pastor used an illustration. He said Billy Graham is probably the most well known Christian evangelist on earth. Can you imagine what it would be like if he was baptized in the Holy Spirit?

At the time, since I was Pentecostal, his illustration was very effective, but now I see just how flawed it really is.

Tom