Thanks for the input so far guys. I do have some jewellers rouge which I purchased to polish up the windows, hadn't thought about whther that might be usable to take out the reg #s, might try that though agree it might be a bit of a tall order
Ivor, that sounds like a workable plan, though one of the few tools I haven't got is an air (or electric) polisher - at least not the type I think you mean (the type you would buff out new paint with, right?). Do you think an electric car polisher (light duty, that you'd apply wax with), a D/A sander or a drill attachment would achieve the same end? As far as the cutting compound, is there a particular grade or something I should use? Would I need a different grade for the 'de-etching' and the rest of the window, or just more time?
I do have some scratches elsewhere on the windows so maybe could kill two birds with one stone? I thought conventional wisdom was that anything deep enough to be felt with a fingernail was deep enough to leave distortion if you polished it out? Not to mention reducing the thickness of your glass?
If you did not have that problem this sounds a promising method.
Re-blasting I could do but again wouldn't want to further blast out the old numbers - that could be difficult to mask off for example. But would certainly consider
Mark, I hadn't heard of micro-mesh. Is that suitable for glass as well as acrylic? Presumably it wouldn't be practical to use that to polish the rest of the window as well, I assume it is a manual process (manual = good control

though labour intensive

)