On her soul. On his back. In a life, on a bookshelf, atop shoulders.
Do things that leave a trace. Whether it is founding a thought that provokes a smile, the giving of a gift that is loved or the leaving of teeth marks that illuminate some temporal, sordid need.
Add to someone. Leave them better off than you found them. Even if it is practically imperceptible. Even if it is fleeting. Even if you have no reasonable expectation of reply. When you think about it, the evidence of your presence that you create in someone else’s life is nearly all you are.