Bruno is a hearing child and was 13 months when his parents and I started signing with him. We originally started signing in view of me speaking French to him, which would have added to his Polish and English. In the end, we decided against the French but in favour of signing, as a bridge between his two languages, and as a means for him to convey his needs.
We started with "more". We would sign it every time we said the word. About three weeks later, Bruno signed "more" himself, at first with no relation with the situation, and then he started to really get it and ask for more of everything, to see what effect it would have. One day, as I got to the end of a book I was reading to him, he signed "more". Not only had he understood that he could get more of something physical, but he could also ask for something to be repeated!
The second sign we introduced (a few days after he had mastered "more") was "potty". He was very much into going to the potty at the time and he used the sign frequently. More signs were quickly added as we felt that they were a very useful tool for expression to have: milk, drink, music, book, walk, baby, shoes, monkey, bird, sleep,... All I can say is that he has taken to it like a duck to water and is really enjoying it.
Bruno is now 20 months and he has about 20 signs in his repertoire. Everyday he shows me his need for more signs as he discovers more of the world. He is now starting to orally repeat words more often, and his favourite one is "bye-bye", which can take a lot of different meanings: goodbye, shut, finished,... Even though he is improving fast with his pronounciation, he still has a long way to go until he can talk. In the meantime, signing allows him to communicate his needs and feelings in a way that would have been impossible otherwise.
Our interactions are so enriched by baby signing. He doesn't cry or get frustrated when he wants us to know something, he just signs it. We seem to understand each other so much more now that he can sign, and we are certainly more in tune with each other. Bruno feels like a part of the household, being supported and encouraged in his progression towards talking.