The ISS is the International Space Station, where Dawson has been since April 4 of this year. She's talking about flying into space because it's true - maybe you could, one day, no matter if you are deaf. And she said it in American Sign Language, from the Space Station. You can watch the video here.
According to the above-linked article, in 1992 Bill Readdy also signed a message from STS-42, a Space Shuttle Discovery mission. That video is at the link and you can watch it here: