Just popping my head in... I have a younger brother with Autism, and I'm a behavioral therapist for
autistic children in the US. (and I'm expecting in January!
yay!) If any genetics theories on autism are right, our chances for a child on the spectrum are high as my husband has a sister with autism as well...
Signing is great!! Even if it seems that your child is not picking it up.. keep doing it. He/She might not be able to do it physically with their own hands for many reasons (muscle tone all the way up to just being stubborn, lol) but if you continue to pair your words with the sign... it helps them understand.
Pictures are awesome too... each child will respond differently to different communication methods. You will in time figure out what works best for your little one. But I couldn't advise you enough.... don't go back and forth between methods!! Do them both at the same time if you like... but don't try sign... then go to picture... then back to sign... then back to picture. Consistency is key!
You guys are amazing parents! Keep up the hard work!