A symbolic action or element is a special ritual that you may choose to include in your ceremony.
These can be incorporated to signify special meanings. There is no end of actions that you can use to represent something special in your relationship/family. They can be made to suit any ceremony and can involve as many people as you want.
Below are just three classical, simple but very lovely ideas but there are many many more.
I also love to adapt rituals based on your story and family history and create something that reflects you.