What is the definitive guide to baby sign language by Janis Elspas?

The available content does not show a specific “definitive guide to baby sign language” authored by Janis Elspas under that exact title. There is, however, a reposted question about the benefits of teaching baby sign language, suggesting interest in the topic, not necessarily a full guide.

If you saw that phrase somewhere, it may have been marketing copy or a blog post title rather than a published book or formal guide.

Where did you first see “definitive guide to baby sign language by Janis Elspas”?