As promised, here is the video showing the words Silas knows in sign. They are presented more or less in the order that he learned them.
So, there you have it. The boy says no real words vocally, though he is starting to parrot us more and more often, especially if the sounds we're making are goofy. For instance, Silas and his Dad do a great monkey impression. For a while, he'd repeat "uh-oh" to us, but we can't get him to do that anymore. The sign language, however, appears to be sticking. He learned all 6 of the signs you see in the video just after his first birthday, over a mere three week period.
Note that one of the signs he knows very well and had no problem learning is "kitty." So, he says "kitty" but not "mama" or "dadda." And believe me, we have tried to teach him to say mama and dadda both vocally and in sign. He doesn't seem that interested, but he'll catch on eventually. He does babble incessantly and the sounds mama and dadda come up a lot. He says "mamamamama" quite a bit, especially when he is complaining and wants something. At these moments, I delude myself into thinking he means what he's saying. Truthfully though, the context just isn't quite there yet, despite the fact that if you say "where's mama" or "where's daddy" he'll laugh and turn to the adult in question.
We are continuing to introduce new signs including bib, eat, doggy and of course, mama & dadda. Hopefully, he'll be adding these to his repertoire soon. Baby signing rocks!