Apparently there's been some research that shows that toddlers can learn to communicate with sign language more quickly than some of their verbal skills develop. There are classes that parents can take with their kids to help teach a simplified version of sign language, called "baby signs".
Charlotte is making up her own little sign language. It's not that she's not verbal; she actually says a couple of dozen words, and is starting to work on 2 to 3 word phrases. In addition to her words, she has added a couple of signs of her own.
The first sign she ever made was to point at things. This started well before 1 year, and meant either "I want that" or "I am paying attention to that". I think a lot of babies get this one early. She then learned to nod her head "yes" and "no" early also..only lately has she started verbalizing her "no"'s.
The next one she made up was for brushing her teeth. She takes her index finger and sticks it in her mouth, imitating the motion of a toothbrush. She was probably 14 months or so when she started doing this one--until then, she had no teeth and we weren't really brushing her gums much. Usually she says it in response to us talking about brushing teeth, though she's been known to hand one of us a toothbrush and make the sign--she's starting to take care of us like we do for her--feeding us, and brushing hair and other various tasks.
Most recently, she's come up with a quasi-sign for Cookie Monster--she puts her hands to her mouth and makes a gobbling sound like Cookie Monster does when he's eating cookies. If you mention a frog or a rabbit, she bounces up and down and makes a growling sound that's vaguely a low, toad-like "ribbet" (which must sound a lot like rabbit, and they both hop, so they go together I guess). She's also learned how to motion "shh"--Especially when someone's lying down like they're sleeping, she puts her finger to her lips. Of course, while she's there, she also tends to pick her nose. She's nothing if not opportunistic....