What two cultures have used a form of sign language?

It's impossible to say definitively which two cultures were the first to use sign language, as sign language has likely existed in many cultures for centuries, predating written records.

However, two cultures with documented histories of sign language use are:

* Ancient Greece: Historical accounts suggest the use of sign language among deaf individuals in ancient Greece. Philosopher Plato even mentions a specific sign language used by the deaf in his writings.

* Native American Cultures: Many Native American tribes developed unique sign languages, often used for communication between different tribes, particularly when languages were different. The Plains Indian Sign Language is one well-known example.

It's important to remember that this is just a small sample of the many cultures that likely developed sign language. The development of sign language is likely as old as humanity itself, with countless cultures and communities using it for communication.