To the youth of today, the moon landings must seem like something from an ancient time, which maybe goes some way to explaining this 'Olde Worlde'-style signature. In any case it seems likely that this combination of 17th Century Armstrong signature and 1994 cover is unique.

Unfortunately, even the extreme antiquity of the signature doesn't explain why it was signed "Keil" instead of "Neil". My theory is that the feathery end of the quill tickled Neil's nose causing him to sneeze as he was writing the "N", but we'll probably never know for sure.

Rating:
B for effort (found a fountain pen to sign with)
B for artistic merit (fancy penmanship)