Greetings, AFAICS there’s currently no way to insert a marker through any of the menu items; as a result the `Ctrl-M` shortcut is hardly discoverable (though there _are_ menu items to skip to the next/previous marker, which are very convenient).
I’d suggest adding that command to either in Edit>Insert submenu or to the “Search” menu where (for some reason) other marker-related commands already are to be found.
Additionally, it would nice to have it in the editor’s context menu.