Very odd that they are painted. Stick-ons have been available for decades.
Not sure what to use but I know what not to use and that is something like Jasco Paint Remover. It will distort the gel coat.
If they are on a flat surface you might consider color sanding them off with some 600 grit. If they are like mine, they are mounted on a concave surface which would not lend itself to sanding.
Hopefully someone has some better and effective ideas.
I know this is an old thread, but I recently did this and it worked like a charm. I started with 600 grit wet sandpaper, then 1000, then 1500 literally 5-10 min job
