Will the lettering harm my painted surfaces of my vehicle?

NO!

But a couple of concerns.

Do not apply lettering to “fresh” paint. Check with the painter for curing time. The paint should be cured before installation.

If after many, many years you remove the lettering, the paint underneath will not have seen any “wear and tear” and will usually have a better gloss (like the day installed). And on some paint colors (i.e., red), fading of the paint where the lettering was not installed is noticed for the first time. But usually a little wax or buffing solves this problem.

Besides these two concerns, the lettering will not harm your paint in any way.

Have another question about decals, signs, lettering,
or stripes?