The e-mail saying "You've now been vouched on Mozillians.org. You'll now be able to search, vouch and invite other Mozillians onto the site." should indicate who did the vouching, or at least say that one can find out by editing (!) one's profile.
This is a duplicate of this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=842661
QA verified duplicate