To sign supermarket, we first sign eat by placing our dominant hand in front of our mouth and quickly pulling away. The next motion consists of the sign for shop or store. Both hands parallel to your neck with fingers together moving back and forth.
We use this sign contextually when we take our babies with us to run errands. This is a really fun sign. We can do it prior to leaving the house to create expectation and upon arrival to the supermarket or grocery store.
Babies love supermarkets. A shopping trip is a great opportunity to enhance their vocabulary and teach values such as patience.