I'd go further and say they need to do the same thing with their vehicles, like in Europe. Police officers and their cars are for public safety, and should be highly visible.

Here's a typical Swedish police car: http://www.wired.com/images_blogs/autopia/images/2008/12/15/...

I think the intention in the US is that cop cars have to be less visible so that they can catch people committing "crimes" in order to fill quotas. The policy should be shifted to prevent or deter people from acting badly, and you can do that be just being more visible.