Each Indian tribe had a different language. Many Indians never learned any languages except their own. Do you know how Indians from different tribes talked to each other? They had two ways to talk without sound. One way was by sign language; another way by signals. Sign language is a way of talking by using signs. Indians used sign language when they met strangers. In this way, they could find out whether the stranger was a friend or an enemy. In Indian sign language, signs were made with the hands. One sign meant "man". Another meant "horse". To tell the time of day when something happened, an Indian pointed to the sky. He showed where the sun had been at the time. Indians usually used signals when they wanted to send messages to someone far away. To make signals, an Indian might use a pony. He might use a blanket. Or he might use smoke, a mirror or fire arrows. To signal that he had seen many animals, an Indian rode his pony in a large circle. Sometimes the Indian gave a signal like this and then went away to hide. This meant that there was danger. The blanket signal was visible from far away. An Indian held the corners of a blanket in his hands. Then he began to swing the blanket from side to side in front of him. An Indian could send many different signals with his blanket. He could also send many signals with a mirror. He usually used the mirror to warn someone of danger. Of course, mirrors could be used only when the sun was shining. At night, Indians used fire arrows for signaling. Now you can see that Indians didn't need to learn each other's language. They could talk to one another by using signals or sign language. Sign language is  _  .
a language only for Indians a way of taking by signing on paper a way to express one's ideas by making gestures a secret way of talking to strangers