"This gentleman was a genuine part of American history," author and collector Anthony Pizzitola said.
Pizzitola says he knows quite a bit about Armstrong. The Houstonian and history buff has been collecting the first man on the moon's autograph for 30 years now.
"It's so unique, simply because it is the holy grail of autographs among collectors. He was the first modern day Christopher Columbus," Pizzitola said.
Pizzitola wrote the book, "Neil Armstrong, the Quest for his Autograph," and he has one of the largest collections of rare Armstrong signatures, including pricy signed prints of the astronaut in his white space suit and in training photos. They're valuable since Armstrong stopped signing autographs in 1994.
"Now his death has catapulted that off the launch pad to 20-30 percent higher prices," Pizzitola said.
But now the potential demand for Armstrong's rare autograph has collectors like Pizzitola sending strong warnings about fakes. So how can you tell if your autograph is real?
"It is very tough to distinguish between an original Armstrong and a fake Armstrong," Pizzitola said.
Pizzitola says one way to spot a fake is by looking at the American flag patch on Armstrong's white space suit photo. He says Armstrong always wrote above or below the flag, not floating around.
Pizzitola says you should also be careful for reproductions produced with autopens. You can't tell at first glance, but Pizzitola says the autopens leave squiggly lines in the signature.
Pizzitola is a member of the Universal Autograph Collector's Club. He says the group has experts who can authenticate signatures on many items, and it is free of charge in most cases.