One thing that at least some rich people will pay for is status symbols (expensive watches, sports cars that will never exceed 100mph, mansions with rooms that are used only a couple of times a year, $500 t-shirts). Status signaling is ultimately a zero-sum positional arms race that can lead to some pretty ridiculous conclusions(1) and doesn't really leave anyone better off (other than, perhaps, luxury goods suppliers).
The bad version of this idea would be a special ID card and/or bumper sticker or t-shirt or watch that was given to top-bracket taxpayers. It would have to be reasonably hard to forge (or at least as hard to forge as, say, a Rolex) and able to be either displayed publicly or flashed discreetly in situations where one wants to assert status.
Another variation could be some kind of property tax where certain sub-neighborhoods would have exceptionally rates, say 100x what the ordinary tax on the land and improvements would be. Then people could signal status by living or staying in those areas. (This is actually not too different than somewhere like Manhattan or San Francisco currently, except the windfall is going to existing property owners rather than the government).
The nice thing about status symbols is that, like fiat currency, they can be rather cheaper to produce than what their value to the status-seeking public is. That is the government could potentially retain a very high seignorage, as it were, on this stuff.
Ultimately it would have to be determined whether the status symbols could be legally transferrable, and what, if any, penalty there would be for forging them.
As an aside, it strikes me that this sort of thing would be extremely similar to fiat currency, maybe identical.
[1](http://www.google.com/products/catalog?client=safari&rls...)