Sandals is signed like shoes, but with an added element (depending on the type of sandal you are referring to).
To sign sandals, form both hands into fists and bump them together a couple of times in front of you. Then open your non-dominant fist into a number '4' hand, and follow through by swiping your dominant index finger twice between your non-dominant fist's index and middle fingers, as if indicating the thong of a sandal.
Teach your baby or toddler the sandals sign once they have mastered the concept of shoes and are ready for variations of footwear.
Teach this sandals sign along with the other flash cards pertaining to footwear once your baby has grasped the basic concept of shoes.