Flathead camshaft 5-T question

[skidmarks]

I tried the search and brings up a number of post about 5-T camshafts. Common number found on flathead camshafts

But the question I have , I haven't found any information on.

On the opposite side of the slot for the distributor drive is another stamp. Circle with the letter F in the center and what looks to be the number 4 to the lower right of the F.

The 4 is very small and hard to see. I tried to take a picture but it's hard to see.

Looks like it was stamped all at once. Does it stand for anything or just something ford stamped in it?