There is such a thing as conspicuty tape. It is reflective tape used on signs and long trailers. No technical reason you cannot apply a strip to your car, unless traffic laws prohibit it.

Although reflective tape might be helpful, now that electronic components are getting smaller and cheaper it might be possible to make a tape containing both solar cells and bright LEDs in a continuous strip with an adhesive back. Perhaps this is still not cheap enough at present but we are probably on the way.

Reflective strips work well on squad cars in rural areas. . .You can see them a mile away.

I do think in large cities the LED concept would be overkill. . .Think Las Vegas on wheels. It would be interesting tho'. The reflective strips, on the other hand, get washed out by all the lighting in cities so you don't really notice it.