M24 bottom floorplate built by Dakota Arms. They were a Remington Arms subsidiary company before the first bankruptcy. Afterwards, Sunny Hill Enterprises Inc. took over production for Remington M24 floorplates.
Dakota Arms used a 2-piece construction process for their version of the M24 floorplate, with the parts fillet welded together. This required a special Magnaflux inspection process, with a stamped "M" proofmark after certification applied onto the weld joint.
(The Sunny Hill variant was not welded, instead it used 2 allen screws. Apparently this did not require Magnaflux inspection, and would not have the "M" proofmark.)