Removing lettering over paint is tricky. My standard tool is a razor blade and extreme care and patience. First you absolutely must dull the ends of the razor blade. I use a sharpening stone to round the ends off including rounding on the angle of the blade itself (hope that makes sense). If you do not do this you will scratch the surface. If your lettering is vinyl you can lift an edge with the blade and slowly peel it off. You can warm it a bit with a hair dryer or heat gun but sometimes this makes things worse as the vinyl will come off and leave the glue and might soften the paint underneath.
If the lettering is paint I would first try the razor blade, if no success I would sand with 400 wet, or even finer and finish off with 1000.
There is a good product for removing glue. Goo remover maybe, can't remember. I have a bottle on the boat.
Good luck, take your time, test a small area first, and be very very careful.
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Currently in Long Beach, CA