Book: The 5-Minute Linguist
Chapter: 31. Do Deaf People Everywhere Use the Same Sign Language?
Sign languages have all the linguistic features that spoken languages have (except sound). Sign languages have complex grammars, so that words can be strung together into sentences, and sentences into stories. With signs, any topic, from concrete to abstract, from street slang to physics can be discussed. Moreover, sign languages vary, just as spoken languages do.