Our body is the first channel to relate with the world, through it we feel love through hugs and kisses and also pain when we prick a finger, fall, among others. That is why we interpret the world according to how the body feels. Each external physical mark will reach the inside with some emotion, that is why tattoos or piercings that have been made by slavery are usually marks that are transmitted from generation to generation, I am sorry that your grandmother had to live that experience, I can imagine how it must feel to be part of that story.
It is very responsible and mature of you to wait and know that a tattoo should be taken as something important and special.
Thank you for @marsdave sharing your experience related to the subject.