After the completion of the Mercury and Gemini projects, NASA wanted a way to promote greater awareness among its employees and contractors of the impact they had on flight safety, the flight crews and their missions.[4] NASA wanted to use a symbol for spaceflight that would be well known and accepted by the public, similar to the recognition received by the United States Forest Service's Smokey Bear.
    The idea for the Silver Snoopy award came from Al Chop, who was director of the public affairs office for the Manned Spacecraft Center (now called the Lyndon B. Johnson Space Center). He wanted to create an award featuring Snoopy as an astronaut to be given by astronauts in recognition of outstanding contributions by employees.[5]
    Charles M. Schulz, who was an avid supporter of the U.S. space program, welcomed the idea of using Snoopy for the award. Schulz and United Feature Syndicate (the distributor of the Peanuts comic strip) agreed to let NASA use "Snoopy the Astronaut" at no cost.[4] Schulz himself drew the image the award pin was based on. He also drew promotional art for posters to promote the award program.[5]

“ The command module was given the call sign "Charlie Brown" and the lunar module the call sign "Snoopy". These were taken from the characters in the comic strip, Peanuts, Charlie Brown, and Snoopy.These names were chosen by the astronauts with the approval of Charles Schulz, the strip's creator,who was uncertain it was a good idea, since Charlie Brown was always a failure. The choice of names was deemed undignified by some at NASA…”

https://en.wikipedia.org/wiki/Apollo_10#:~:text=The%20comman...

https://www.chrono24.com/search/index.htm?dosearch=true&quer...

http://spaceflownartifacts.com/flown_silver_snoopy_awards.ht...

seems like in the apollo era crew carried a few in their PPK (personal preference kit), and in the later shuttle era they regularly carried 500-1000 pins per mission.