When we defined the 0x50 notary signature, the old 0x40 from 1991 was
the insipration for it. 0x40 was defined in 1991 as more or less what
the 0x50 sig is defined for today. Now we have both the 0x40 and
0x50, and the 0x40 seems rather underdefined to me.
For starters, there are no hashing rules specified for it, so how do
you make one? Since both the 0x40 and 0x50 get a target subpacket,
one could infer that they are similar, but there is nothing concrete.
I'm not necessarily requesting that 0x40 be fleshed out and clarified:
I'd be just as content to see it dropped. If, as I assume, the 0x40
is just the same as the 0x50 with a different (human) interpretation,
then perhaps we should just drop it. If people want to assign human
interpretations to their signatures, let them use notations.