McGrath-Hamin (?) Top Hat Brooch Flea Market Find $2.00

After much too-ing and fro-ing on the web, I came to the conclusion that this must be a McGrath-Hamin piece. At first I thought Miriam Haskell but figured that was too much to hope for, lol~! Her designs tend to lean in the Victorian direction, and this brooch is more Rockettes style. :-)))
The "MH" looks like it was done by hand.

The rollover clasp itself is even stamped - twice.

Maybe I am completely mistaken, too...it's been known to happen from time to time.
:-)))))
I didn't find one exactly like this in my Image search.
I don't know what that "3M" mark is nor do I know what that small mark on the back, behind the pin, is supposed to be.

Thanks to anyone who recognizes those marks and can set me straight.

Thanks for looking/loving, friends!