I think that'll be bounties.

I definitely saw jldugger put a 500 bounty on [this question][1], and quickly clicking through some of the others, they look like bounties as well.

You can go on a users profile, go to the reputation page and click the huge negative bar in the chart and that will reveal a bounty was offered.


  [1]: http://serverfault.com/questions/110964/can-i-get-ad-to-authenticate-via-another-ldap-server