Those below are the famous apes. They have proven that not only humans can do sign communication.
http://en.wikipedia.org/wiki/Washoe_%28chimpanzee%29
Washoe is a chimpanzee that can do American Sign Language (ASL) to communicate with the scientists.
http://en.wikipedia.org/wiki/Kanzi
http://www2.gsu.edu/~wwwlrc/biographies/kanzi.html
Kanzi is a bonobo that learned lexigram through her mother and other scientists. His life's story is very interesting. According to the second site of Kanzi, Kanzi's vocabulary steadily increased. Today it is well over 200 words productively and 500 words receptively.
By the way, bonobos are the only apes that truely practice the "make love not wars" thing. They use sex gestures to ease off aggression, fighting and so on.
http://en.wikipedia.org/wiki/Koko_%28gorilla%29
Koko is a gorilla that knows more than 1,000 ASL words. And it's so cute to read that, "Koko is also the only non-human known to keep pets of a different species: she has cared for several cats over the years." (http://en.wikipedia.org/wiki/All_Ball)
http://en.wikipedia.org/wiki/Congo_%28chimpanzee%29
This chimpanzee can paint and his paintings are being sold up to 1,500 dollars. How amazing.
http://en.wikipedia.org/wiki/Nim_Chimpsky
He could use ASL like Washoe. Check out for the list of what he could say; they're so cute.