Denise it is not the letter m before the g on the patch, it is the greek letter mu. The letter mu, which as a prefix is referred to as micro, represents a unit of measurement on the order of one millionth of a gram. Which means they were doing experiments on very, very small amounts of material and how they behave in zero-gravity.
As a proud member of the NASA family for almost 30 years, I can tell you that another accident of the shuttle fleet is almost more than we can bear. Personally, I was devestated, and I am afraid for the future of the agency.
May God bless the crew of Columbia and their families!