I took two terms of signed English in college, and one of American Sign Language. ASL is its own language, like French, and has its own rules and grammar. Signed English takes ASL and adds initial letters to the word (signing the word free with the hands held in the shape of an "f" for example), uses the same sentence structure as English, and adds some verb forms that ASL doesn't have, like "ing." I don't think many deaf people really use Signed English, though. My understanding was that it was a well-meaning attempt to improve deaf people's literacy, because in essence they are learning two languages: ASL and English. Interestingly, even though it is a language of movement, I think sign language must live in the part of the brain where spoken words do. When I lived in Germany I would sometimes search for a word in German and come up with a sign instead.
I learned sign language because my freshman crush had a best friend that had been on the scene before me. They learned the alphabet so they could say things to each other and torment me. (Full disclosure: Actually, I think the best friend was probably gay, but didn't know it. He was certainly jealous of my relationship.) Then they learned some signs, and I learned some signs, too, and then I took three terms.
When I worked at the admitting desk of a hospital about six or seven years later, a pretty young red-haired woman came to the counter. She was signing and I was trying to follow. I thought she said she wanted to change, but she really said she wanted to die. (The signs are kind of similar, both involving holding your hands out flat and flipping them over.) I gave her pen and paper and she wrote down what she meant. She said she was in a shelter because she had been raped by someone she knew whom the police were still looking for. That the hospital that had treated her after the rape hadn't had a sign language interpreter for her, which horrified me. And then she had to leave because it was time for the shelter's curfew.
I called the woman's crisis line, and somehow we managed to get an interpreter and a counselor and this woman all together in a room at the hospital a night or two later. The woman wanted me there, too. She talked about how she had been raped by her friend. She signed and vocalized a little, as people do who have been mainstreamed. I had to stay late and missed my bus. Afterward the sign language interpreter gave me a ride home after I asked if she would. (Full disclosure: actually she didn't give me a ride all the way home. She dropped me off about a mile from my house and I walked the deserted streets the rest of the way, the sound of my heels echoing in the dark. Looking back, I should have pushed it. Why did I think I was immune to being raped myself?) In the car she told me that there had been something odd about the woman's signs. She thought the red-haired woman had come to signing late. I could see what she meant, because I had been able to follow the woman's signs. And sign language is different than most languages. You can usually sign better than you can understand sign, unlike say German, where I can understand better than I can speak myself.
Several months later, I saw the red-haired woman on the bus. I signed 'hi" to her. And she said "hi" back and didn't use her hands. We both got off at the next stop and talked. I learned that she wasn't deaf at all. She had deaf friends and had learned sign language. And after the trauma of being raped by her friend, she had temporarily lost the ability to speak. It was a surreal moment.