Many daycare centres have at least one teacher that has basic sign abilities. Depends too on the age of the child. If they are very young then they likely only have learned a few signs and the provider could be taught along with them. I would think sign was harder to incorporate than another foreign language because the child would be able to use other cues to get what was needed and would soon pick up the words of the other children. In the case of sign non of the other children would understand either.