A smile is an invitation to be met. It is an invitation to be held in the moment.
Meditation is often an exercise in meeting ourselves in the here and now, which can reveal a lot. As we practice smiling with all that arises in a sitting, such as thoughts and emotions and sensations, we allow ourselves to be present with ourselves.
The shape of a smile resembles a bowl; indeed, a smile contains. It contains the fullness of who you are.
Happy meditating.