I think you're right about the index point - but it is upside down in this photo, which might have made it harder for the OP to figure it out. All a matter of perspective, eh?I haven't used that exact rest, but have used similar rests. It's probably an index point for your stock so you can ensure your rifle is sitting in the exact same place in the rest every time.
Flip it up and lock it. It helps cradle/stabilize the stock.Bought a lower budget front machine rest, a Protektor Model. No literature of any type in package. Zilch. Happily, it seems simple enough, except for this thingy hanging off it. Can somebody school me on this thing, please?