Hugs are good for demonstrating love. And they offer an opportunity to check out how tall a grandchild is growing, which often leads to giggling.
Cookies are good for demonstrating love, especially if the grandchild is allowed to help bake them. If that's not possible, it's fun to receive them in the mail -- wrap each cookie individually to give it the best chance for crumb-free delivery -- or a tea party with freshly baked cookies says “I love you,” especially if you dress up for the occasion -- even if the costumes come from your dress-up box.
Letters and notes are good for demonstrating love, because who doesn't like to get mail? Enclosing a photograph of something you did together is an added bonus. Or you might include a poem, and invite your grandchild to memorize it, too, so that you can say it together when you see one another the next time.
It's not so much what we do to demonstrate our love, it's that we do something. Grandkids respond to love like sponges respond to water: they soak it up.
It's a mutual blessing.