WASHINGTON — (CNN) Friday marks POW/MIA Recognition Day, meant to mark the sacrifice made by American prisoners of war and those still missing in action.

One of the places where American prisoners and missing are commemorated year-round is at the Vietnam Veterans Memorial in Washington, where since the memorial was dedicated in 1982, visitors have have left tokens in memory of the fallen, the imprisoned and the missing.

But what happens to those items after visitors leave?

The wall is under the care of the National Park Service, and NPS staff has collected and archived the majority of items left there.

And though there are a number of other memorials on the National Mall, the NPS only regularly collects items left at the Vietnam Memorial.

“We weren’t sure what to do with the items at first. There were a couple of maintenance people who felt too guilty to throw away the things that they were finding there, and so they kind of squirreled away the items and kept them,” NPS Museum Technician Janet Donlin told CNN.

“And in 1984, our regional curator found out that this was happening and she decided to make it an official Park Service collection.”

Once collected at the wall by NPS employees, the items are taken to the Museum Resource Center in Maryland.

The Center serves as the storage center for NPS collections in the National Capital region and holds more than 40 museum collections.

To date, more than 1,400 boxes are dedicated to items from the Vietnam Memorial.

Donlin is the museum technician in charge of cataloging and preserving the Vietnam Memorial collection.

She estimates that, after more than 30 years, there are hundreds of thousands of items.

The only thing the NPS doesn’t keep are things like wreaths left by school groups — there are just too many.

“The biggest category of things that are left at the wall are what we call documentary artifacts — basically documents. It’s letters, poems, notes, pictures, collages,” Donlin said.

The collection includes such unique items as a race car hood, mannequins, a helicopter blade and a motorcycle.

Per instructions from the Wisconsin veterans who constructed and donated the motorcycle, it is not to be ridden until all of the state’s missing soldiers are brought home.

There are still more than 1,600 Americans missing from the Vietnam War.

POW/MIA Recognition Day is regularly marked on the third Friday in September when the President traditionally signs a proclamation.

To see some of the items left at the Vietnam Memorial for prisoners and the missing, watch the video above.