Welcome to the Forum, Ole Craw! You've got a nice first year Model 586. As stated above, the triple-alphanumeric s/n's began with AAA and the L-frame Model 586/686 revolvers. There was a S&W factory recall on those early models, which I believe will still be honored if you're concerned and would like to send it back to S&W (the M stamp indicates the mod was performed). But of course contact Customer Service before taking action. BTW: you didn't mention the bbl length, or post any pics. We like pics.
Congratulations and enjoy!