The famous Belgian stamp block issued for Apollo 11 is widely known as the only commercial signing Neil Armstrong ever did (aside from some charity items such as the Naval Aviation prints) in his life.
The total amount is most likely near 1000 such signed stamp blocks (due to huge demand John Glenn and Neil Armstrong did an extra quantity while the other 18 astronauts signed 500 stamp blocks each) done in the very early 1970s as confirmed to me.
Few people until now were aware that German dealer Hermann Sieger (who was behind the stampblock deal negotiated by Walter Eiermann) also had 30 Belgian stamp blocks with a first day postmarker "Gent" signed by Neil Armstrong making these the rarest commercially signed Armstrong item on the market.
We were lucky to get our hands on two such samples available now on spaceflori.com along with many other new items!
Aside from these we also have two "regular" Armstrong signed stamp blocks available, one signed in blue ballpoint pen and the other one with a thin fineliner which is much rarer. (for those collecting varieties).