Thanks - had a look but this ain't easy. No audible warnings either - just POIs on the map. The road angel or similar is probably the way to go. I noticed on their website that they have discontinued the EVO (the non map display one) but stock may be available via Harvey Norman. At $299 its cheap insurance.
I reckon some of those "James Bond" revolving number plates are the answer
I could just push the button whenever I speed to spin the plate around to read KME-123.