This was mentioned briefly in another thread & I suspect some may wonder what we're talking about. There's another name for this, but I can never remember it .....
Anyway....
With very hi-gloss paints, this isn't an issue, but with acrylics .........

When you apply a vinyl paintmask over most acrylic ( you may call it latex, but if it doesn't say 100% acrylic on the can, it's junk) the "roughness" of the finish will let your next colour bleed under the mask. Cleanup can be tedious, usually done with a #1 lettering quill. Here's how to avoid this ......

It's only the FIRST coat that will bleed under, so, using the same colour as your background, use an artist's "flat" brush, & seal the "cut edge" of your lettering (or whatever) . Don't just pull a line overlapping the edge ... brush it across at 60* to 90*. What you're doing is damming subsequent coats.You'll still have some bleeding, but since it's the same colour, it can't be seen. You'll have very little cleanup ....

One caveat ..... If you are using high gloss acrylics, you have to remove the mask while the paint is wet, otherwise it will "bridge" & tear off chunks you need left on there. If, for instance, I want gloss white lettering, I'll put an undercoat of satin white, then top it with hi-gloss.
Also, if you're using an oil based enamel, again it will "bridge", so you'll need to pull the mask wet. Once you know this, you can pre-cut your mask into sections that make it easier to weed without fear of loose ends falling into your wet paint.

I'll edit this later & add pics, if anyone isn't clear.