With the help of Enrico and the Debian Listmaster Team -and in particular Alexander Wirt: thank you very much! - the spam reviewers of the Debian mailing lists have been added to the list of Debian Contributors.
While some statistics about the reviewing job already existed, adding these data to the Debian Contributors list is another little step to map all kind of Debian contributions.

Wondering what exactly is the job of the spam reviewers?

It consists in checking all the messages of the Debian mailing lists reported as spam: if a message reported as spam gets three reviews as spam (and none as ham) it is removed from the archive.
Only DDs can do this: if you are one check here how to do it.
But there's one - and probably more important job - that everyone can do: report spam. When a message is reported as spam by 5 or more persons, it will make to the reviewers' queue. There are some organized spam cleaning efforts you can join: here there's a list of them, while on this page you can find more information on the whole process.

Wondering what exactly is the Debian Contributors list?

It's a brilliant effort started by Enrico to map all kind of contributions in Debian.
You can read more about it here and here.