It's a good idea for an add-on service, which I think people are already working on: an independent database that keeps track of "dirty" coins.

Similar to the address labels on Blockchain.info, I guess. I like this idea better because it lets people choose to participate.

For example, the DPR coins might be attractive to someone who wants them as a memento of Bitcoin history, but to someone else they might be unwanted as a symbol of government intervention. Letting people see that those coins have that history, if they choose to look it up, and then letting them decide for themselves if that affects their value one way or the other sounds like a much better solution than simply telling someone their coins are stolen.