It's very sad to lose our loved ones, especially if they are taken too soon, or unexpectedly. Wearing a jewelry piece designed to remember them by is a monument to their spirit and the love we still feel for them.
By using their birth data, and building a natal chart piece aligned to their unique birth data. Special stones can also be selected.
You could do this with a parent, grandparent, other relative, friend, or even a pet's birth or other horoscope data (if you don't know the actual birth data).
It just signifies that the person was important to you. Similar to wearing a locket with a picture, it's just to remind you of this other soul's connection to you and that they are remembered.
We can also work up a design combining two or more charts, if that's what you want. Some people do this for mothers with their children's charts, or relationship charts.
You can design jewelry to signify whatever you want. As long as it is meaningful to you, is the main thing.