I have found that using acrylic paint on top of the glass, under the varnish works best for me. For designs my wife cut a template with her craft cutter, and I use a pouncer to apply the paint. The paint seems to run too much on the plain wood, and is harder to sand out any mistakes. If someone were to steal your boat and try to erase the design, they would still have to sand off the varnish and the design. Not as much work as trying to remove the design under the glass, but still alot of work.