Forged Iron Hooked Spike; What's It For?

This is ~8 1/2" long overall, weight is 13 1/2 oz. Cross section is slightly diamond-shaped, with ~1/2" faces; the tab is ~2" long by ~1 1/8" wide, ~1/8" thick, the width is ~3 3/4". At the outside of the U-bend, there's a flat spot, indicating it was hammer-driven at one time.
When acquired a few years ago, it was buried in mud at an old farm site, an' entirely covered with thick, flakey scale rust. I hung it in the weather for a couple years; over that period I 'helped' the scaled flakes to separate as they loosened; probably 2-3 ounces of the red material was shed. An interesting feature is the presence of tiny spots with pinpoint dark centers, best shown in pic 4, that cover perhaps 80% of the surface. They may be significant to those of you that work with iron an' its alloys, shaping it using heat an' hammer...carbon granulation? I dunno 'bout such things, though.
I am clueless about whether it is/was a tool, or part of a farm implement...or even something begun an' not completed; the tab begs for a few holes, to attach this to something. I'm hoping some of you can recognize an' ID this unusual find. Thanks for lookin'!