And all of you are old too.
The blue plate is a Wisconsin Collector plate. Car must be at least 20 years old and pretty much stock as it left the factory. You have to have another vehicle registered in your name, as Collector plated vehicles can't be driven in January.
The benefit to Collector plates is that they only require a one-time registration fee: $200 for your first C-plate car, $150 for every one after. These plates are valid as long as you own the car.