Your suggestion sounds like going back to 20th century technology, when the 21st century version is more efficient, to me.
Although it's still a legal requirement to display a tax disc, they're largely redundant. The roadside cameras which identify tax dodger don't actually read the tax discs on cars. They simply compare the registration numbers to a database of taxed vehicles. Similarly, police officers don't have to carefully inspect tax discs to see whether they're stolen or forged; they can quickly call upon the same database.
If you want to see more uninsured drivers getting caught, you should be calling for more cameras linked to the central insurers' database. While the use of such a system is imperfect (in that it doesn't actually check whether the person in the driving seat is covered to drive that vehicle), it's far more efficient and reliable than the use of old-fashioned paper discs.
Chris