The phrase "sleepy signs" refers to the physical and behavioral indicators that someone may exhibit when they are feeling tired or sleepy. Full definition
If you have a child who does not show sleepy signs (not all children do), you will have to watch the clock, too. (sleeplady.com)
She is counting on your to help her, a baby can not put herself to sleep, nor can she understand her own sleepy signs. (pregnancymagazine.com)
Obviously this won't be the same for all babies, but paying attention helped me understand him better and work with his natural sleepy signs. (evolutionaryparenting.com)