Rose is a compound sign. First, sign the ASL letter R with your dominant hand, then using that 'R' hand, sign very similarly to flower by moving your 'R' hand from one side of your nostril to the other. It is as if you are smelling a rose and really enjoying its fragrance.
Teach your toddler the rose sign when the rose patch in your garden is in full bloom, or when you are taking a lovely spring stroll in the park.
This is a useful flash card taught best in conjunction with other flower- and garden-related flash cards.