Whereas I understand what Sheriff badge is, I didn't understand how to get the Constable badge.
Can anyone can explain me?
Pro tempore moderators are "for the time being" or "temporary" moderators that are appointed by StackExchange staff when a new stack site is in beta before it has enough users to be able to elect moderators. See: http://blog.stackoverflow.com/2010/07/moderator-pro-tempore/
Now that this site is large enough to hold elections, moderators will no longer be appointed and there will be no new opportunities to earn the Constable badge.