I recall there are efforts underway to create a constructed sign language ("consignlang" as in "conlang" - constructed language), an international sign language, which if it follows the teaching methodology of Esperanto, would accomplish a few things.
1) Give you tools to help you accelerate the process of acquiring additional national/ethnic sign languages in the future, should you find yourself in Spain, Russia, Australia, and many other countries.
2) Allow you to be able to communicate on an equal footing rather than an imperial footing with other signers of ISL, regardless of their sign language. To that end, everyone would be able to retain their native ethnic language and know a second language to communicate with EVERYONE ELSE. That way, you are able to share in details the elements of your language and vice-versa without having to know how to communicate in the other person's language.
ISL is really more like a bridge language that preserves your national/ethnic/cultural background and allows you to share it much more easily than you could otherwise.