Responsive parenting is a promising framework for obesity prevention, yet attempts to date have largely relied on parents accurately interpreting their child's cues. Infant signing or "baby sign language" could enhance these interventions by improving bidirectional parent-child communication during the preverbal and emerging language years. In a clinical trial testing, a responsive parenting intervention designed for obesity prevention, we pilot tested a brief intervention at age 40 weeks with a subset of participating dyads that taught the signing gesture of "all done" to improve parental recognition of satiety. In addition, we surveyed all participating mothers at child age 18 months on the use of infant signing gestures in the prior year. Two hundred twenty-eight mothers completed the survey including 72 responsive parenting group mothers that received the signing instructions. A majority of mothers, 63.6%, reported teaching their infant signs in the prior year, and 61.4% of infants were using signs to communicate at 18 months (median signs = 2). The signs for "more" and "all done" were used by over half of study participants and were the most common signs used. Other signs related to eating or drinking were commonly used. Signing intervention group infants were more likely to use the sign for "all done" than controls (63.9% vs. 45.5%; P = 0.01), but there was no difference between groups with regard to the use of the sign for "more" (56.9% vs. 51.3%; P = 0.43). Signing is commonly used by parents of young children and holds potential to improve parental responsiveness and obesity prevention efforts.