I think signlanguage for small children is amazing. I got taught the basics in college for my diploma and used it when I work in a placement with special needs children.
I will defo try LO with it and see how he gets on with it.
I think the problem is, we live in the UK therefore he will go to school here and needs to speak English well, therefore if I speak German the whole time he won't pick English up. Hubby sees him 30 mins a day and at the weekend, that can't be a good basis for learning English properly. If that makes sense. Therefore I speak both languages during the day, I might speak German with him at breakfast and lunch and the rest of the time English or the other way around.
I've been using a little sign language with Sofia. No idea whether she understands or not, she's not repeated one back to me yet but then I probably haven't been that good about using it. The oxbridge baby learn to talk DVD uses baby sign language and Sofia loves it.
Ok, I hope you don't mind me coming back and pushing my opinion on the whole languages bit again
I would strongly recommend that you stick with German. It is recommended by language therapists to stick to speaking to your child in one language, apart from that though let me just share some experiences:
My DH's mother is Mexican, and she spoke Spanish with him until he went to school, his first language was Spanish (although he would hear Italian from his father and family, his parents spoke together in Spanish). His paternal grandmother couldn't see the point in him learning Spanish, and basically forced his mum to stop. So they started speaking Italian all the time when he went to school. Within a year he didn't speak a word of Spanish and it wasn't until he was a teen and spent summers in Mexico with his other grandmother that he learnt it again. Now he is pretty much fluent in Spanish but he's not truly bilingual like he should be, Italian is his mother tongue.
My best friends parents were both Finnish immigrants living in Canada. A lot of the family had moved over and she pretty much didn't hear any English until she went to school, she certainly didn't speak any. English is now her mother tongue, once she realised it was what her friends at school were speaking she stopped speaking Finnish at home and her sister and her started speaking English together. Her parents obliged and spoke English with them. She can speak some Finnish, but she's had to work really hard as an adult to relearn it (once she realised it was a shame she'd not kept it up).
I was an aupair to a French/German family, they always spoke French together. The mother had spoken German with the kids when they were babies but didn't really keep it up and spoke mostly French, she would generally only speak German when she was telling them off! Not surprising they didn't want to learn it.
There are a lot of expat families in the area I live in. In France 99% of the expat parents don't speak any French, yet their children go to kindergarten and pick it up within a few weeks and are soon helping their parents out in the stores! I suppose Sofia is lucky both her parents speak French so that we can help with homework etc, but I'm not speaking it with her at home because she will spend so much of her school years (and beyond if we stay here) speaking French.
Ok, obviously your baby, do it your way! But I just wanted to share, and I think if you truly want him to be able to speak German properly you should stick with it and have faith that he is going to be hearing a lot of English and will not have any issues, he's much much more likely to end up not speaking German.