I have a "two hole bobstay tang" also, although on my steel cutter
it is simply a four inch by half-inch steel plate exiting the stem at the waterline. The upper hole terminates the pin holding the bobstay, and the lower hole (currently empty) is to secure a snubber to bring the "fulcrum" of the chain down to the waterline, increasing the effectiveness of the rode
by decreasing the lever arm of the chain right at the roller at the end of the bowsprit.
That hole has to be four or five feet aft of the roller, so it really makes a difference and it makes the "jerking" of the chain on the bowsprit considerably less. Senormechanico has it right.
If you don't have this sort of setup (or if, as in the above example, it looks corroded and ready to snap off), you can rig a rode bridle
by running rope
rode and hooks on either side of the bow, and down to the chain rode at the waterline.
Earl Hinz and other anchoring authorities discuss all these techniques in their excellent boats.