Look like a really good idea - with a bit of luck most will mis-read it as POLICE as I think intended especially with the blue/white check - well done to Equisafety for coming up with ithis.
... I can only use mine when riding alone however. I generally lead group rides and have found that drivers fly past the other riders behind me and then slow down to read my tabard; the results is that my group can get split from my by a car and thus squashed between all other cars and the side of the road. When I'm on my own though, it's perfect and really works!
Great - so the most effective waistcoat is one that appeals to driver's self concerns and fear of being caught rather than trusting them to behave like sensible adults when they see a horse and rider.