"Gestuno" is a somewhat
outdated term for
International Sign Language. The term itself was created, a rough blending of
Italian words that is supposed to mean "
oneness of
sign languages."
The signed equivalent of Esperanto, it was artificially designed because each country of the world has its own signed language. A universal sign language was discussed at the 1951 World Congress of the World Federation of the Deaf, and the organization established a Commission of Unification of Signs. In the mid-1970s, that group developed the ISL at those meetings, the World Games for the Deaf, and other gatherings such as the 1989 Deaf Way conference at Gallaudet University. Each word was chosen by selecting the most iconic sign from existing national sign languages - for example, the sign for "government" was chosen from a Scandinavian sign language because most fluent signers thought the indication of a crown was the best way to show the concept.
Gestuno/ISL is not actually a proper language, like ASL. Instead, Gestuno is mostly a vocabulary that can be used in appropriate situations; its closest linguistic equivalent is probably Basic English.
Sources
http://www.handspeak.com/isl/info.html
http://www.karenika.com/book/hearing_only.html
http://www.deaflibrary.org/asl.html