The designs were created using graving tools, so it was carved into the die whereas the legends you see here were imprinted using punches into the die. So you would have had sharp engraving tools to literally carve the design into the die and then you would have had little punch tools, (like a blunt screwdriver), which would have been hammered into the die to create a series of wedges and lines which would result in the weird letters which you see.
Why? You ask me. Well, it was much quicker to create a die if you just punched a series of wedges into it. They took colossal amounts of time to make using this technique, imagine how much longer it would take if you had to hand carve every single detail. You could use the same wedge for an I, an R, an H, an M etcetera. You can see this on the reverse of the Henry III above where the same wedge shape has been used for multiple letters.