How to paint on an iPhone case?

I just want to write love on a case but what should I use? Like paint? Or sharpie? Will sharpie rub off?

If you want it to look good and last I would use the following:
Plastic Primer
Spray paint or acrylic paint
Plastic primer
Some tape to seal the parts you don't want to paint
280 sand paper
400 sand paper
Precision cutting knife set or razor blades
And Your mobile phone of choice to paint

1) tape off any parts you don't want to get paint on(or make yourself a stencil) using tape and the exacto knife(or razor blade)

2)Sand down the area you want to paint in this order
280 grain
400 grain

This with give the paint something to hang on to.

3)Spray on a thin coat of primer and let dry completely (read label)

4)Paint your masterpiece and let dry completely.

5) optional sealing coat to make it last.