The Department of Mathematics is using Thawte Personal E-mail Certificates for digital signatures. Signatures allow recipients to check that the e-mail they receive from your addresss actually came from you.

The basic certificate” signs” your e-mail with a genaric “free personal e-mail certificate” that is particular to you, but does not contain your name. Trusted members, those who have their identity certified enough to earn 50 points, get a signature with their name embedded.

There is another reason you may want to get a Thawte Personal E-mail Certificate. When passing back and forth confidential information, if both the recipient and the sender has a Thawte Personal E-mail Certificate then you can also encrypt your e-mail to secure its content.
To obtain the 50 points necessary to become certified, users can then find Thawte notaries who upon certifying the identity of the user can give that user points.