3M is a brand name of a manufacturer…
3M typically makes adhesives and abrasives, so perhaps someone brought it up as a sealant or a gasket compound?
My guess is somebody mentioned it in one of the earlier versions of this thread (which I thought were amusing, albeit a little unnecessarily heated) or in the linked thread, above.
3M really stands for “Minnesota Mining and Manufacturing”.
EDIT: See the next post! John nailed it!