I have in the past bought the oil board stencils for my trucks stars.
However, I get a lot of overspray when the cardboard lifts, or as it does not sit flat.
I tried using masking tape, just a small amount actually, on the painted surface, to hold it down.
I have had mixed results.
Well, this time I tried something different.
I went and bought a 2' x 2' piece of magnetic pvc sheet, the same stuff used to make removable auto signs.
I layed the stencil on the magnetic sheet, traced the outline, and cut out using a sharp box cutter.
Not only do I get a sharper painted symbol/star/hood lettering/serial number, I get a re-usable stencil.
The magnetic mateial conforms to curved hoods too.
The oil board last a few times until the paint makes it wavey. then its even tougher to hold down flat to the trucks surface.
Stick on stencils are also availbel, but, they are only able to be used once.
Anyway, thats yer tip for the day!