<person>George Washington</person> was the first <concept>President</concept> of the <place>United States of America</place> after the adoption of the <concept>United States Constitution</concept>.
That might work, as long as it stays optional.
If we used namespaces, this would be:
[[George Washington]]
[[person:George Washington]]
I have a bad feeling about this. Not really sure why.
A third possibility would be to revive my "category" feature (it's still in the code, but deactivated). It would be more easy to mark the *article* "George Washington* as {{PERSON}} once, instead of making that in every occurrence manually (which would inevitable result in some articles marked up like that, some not).