There is definitely differences in sign language.  For example, American Sign Language is different than British Sign Language.  There are similarities, but they can be considered different languages.

Sign language is not intenational. This site has sign language dictionaries for various sign languages all over the world: http://www.spreadthesign.com/us/

Hello,

I am a BSL native signer but I also do other sign languages (ASL, Thai SL, & Inter-SL).

You make the interesting question! There is one global sign language: most people called "International Sign language" or "Inter-SL".

I do often use Inter-SL to communicate the different foreign speaker or signers like "Eat now?", "Have a drink", "Hello", "You swimming?". I am sure many onlookers will understand that but there are some additional features to tuning for more specific meaningful expressions. I do not think there are the rules or the curriculum for "Inter-SL".  So everybody can learn through their experience how to break the communication barrier even you can try talking/signing to the aliens from Mars.

Well I'm learning American Sign Language because I want teach and be interpret because in my opinion is a language more speak and can give me more opportunities than another with a lot of speakers but just spoken in one country ..."The American Sign Language (also known by the initials ASL) is the dominant sign language, through which the deaf in the United States, in places of expression Anglophone community Canada and parts of Mexico, communicates. ASL is also used sometimes (usually in conjunction with indigenous sign languages) in the Philippines, Singapore, Hong Kong, Dominican Republic, Haiti, Puerto Rico, Côte d'Ivoire, Burkina Faso, Ghana, Togo, Benin, Nigeria , Chad, Gabon, Central African Republic, Mauritania, Kenya, Madagascar and Zimbabwe. Like other sign languages, its grammar and syntax are distinct from spoken languages. It is estimated that ASL is used by some 500 000 to 2 million deaf people in the U.S."

Allen, I think you might be confusing the following:

- Sign Languages: <em>fully fledged visual-spatial languages used by deaf people .</em>

- Gestures:<em> movements of part of the body, especially a hand or the head, to express an idea or meaning.</em>

- Body language: <em>the conscious and unconscious movements and postures by which attitudes and feelings are communicated.</em>