There is an International Sign Language, and before was generally known as Gestuno, now refered to as ISL (International Sign language), as there is an international spoken language namely Esperanto, but as neither is vested in a culture, the probability for it to be widely used is very slim indeed.

Each deaf culture has its own sign language. There may be similarities and deaf people may find it easier to converse if from different deaf cultures, than people using speech but evaluating each sign language by its own merits the differences is fundamental and could not be classified as homogeneous.

Each form of sign language has developed in its own region related to the greater culture of that region and therefore, naturally could not be universal, however visual gestures combined with expressions as an only means of communication, together with intelligence gives the edge to deaf people, in this situation.

Common ground might be found in vocabulary and that is about it. Thinking, in Britain, of hand, there is at least 5 different versions of sign language alone and it has nothing to do with regional differences. Maybe they are overdoing it a bit, but please no comment.

[Rebecca observed correctly:
Quoted from: Yahoo Answer]
"I moved from Hawaii to Virginia and even had to change regional signs. It's same as speaking language...regional differences. Move out of one country where others speak another language and there's yet another signed language as well.