The Vietnam Memorial in DC was vandalized this past weekend. The damage is likely permanent. (See the black substance at bottom part of the Memorial.)
From Red State:
The Park Service employee who talked to me said that the initial diagnosis was that the oily substance had stained the stone. He said another analysis would take place tomorrow.Why do they hate us? Frankly, I couldn't give a rat's diseased backside.
UPDATE: This article implies that the National Park Service Maintenance and Staff believe that the damage is fixable.