Trying to get mom to let me have a tattoo?

I want a tattoo. I don't want piercings although she seems to be a lot more accepting of those. I'll be 19 soon. I want to get my tattoo when I'm 20, but I want her to draw it so it means something more. I don't want a tramp stamp, and I don't want one because other people have them or some BS, I've been planning to get it since I was about 15 but she just isn't coming through to the idea. I don't want to get it without her approval even though I know I can. What should I do?