Do you use ASL signals or ones you have just made up? Watson knows a few ASL signals, "water", "eat", and "outside" (although that one is hit-or-miss.)
I started teaching them because I know my sister's dog will dance at her bowl if she's hungry or thirsty, so you don't always know which she wants, and I wanted Watson to know the difference. Now, if I sign "water" and he's thirsty, he will run to his water dish!