I would have put one of those block "M" logos on my web page, but unfortunately I cannot because I do not want to get sued. The "block M" is a trademark of the University of Michigan, with strict restrictions on its use:

A. Registered Marks. Certain University trademarks and service marks ("marks") are officially registered with the U.S. Trademark Office: the bar "Michigan," the block M, the block M with Michigan bar, the wolverine line drawing, the bar "Michigan Wolverines," the football helmet design, "M GO BLUE," "MICHIGAN" in block letters, a wolverine superimposed on a Block M, and a script Michigan.
The Trademark Licensing Office in the Department of Intercollegiate Athletics handles licensing of these marks. These marks may be used only for appropriate University purposes and may not be altered from their registered design. They may not be used outside the University without express permission of that office. For further information, University units should contact the Trademark Licensing Office in the Department of Intercollegiate Athletics (734-763-4183), or email the licensing director, Kristen B. Ablauf, kbracco@umich.edu.
(from http://www.umich.edu/~gateway/policies/#symbols)