This pill is brownish purple (maroon?), small, round (and rounded), and is marked 30 on one side and has the (capital) letter "M " inside a square on the other... Thanks

I would suggest checking out the information that you might find on the following site or take it to a pharmacist for identification and disposal. The site is good, but not foolproof. But, to be sure, I would take it to a pharmacist. Anyone answering you here runs the risk of the ramifications if they answer and are incorrect no matter what you say the reasons are as to why you are asking.

Below, is the site to which I am referring:

Pill Identifier - Drugs.com

Why are the only questions that you have been asking on this site are about identifying pills, please?