Coins have long been used to honor fallen warriors. In ancient Greece, it was customary to leave coins either on the eyes or in the mouths of the fallen. It was said that the spirits of the deceased would use these coins to pay Charon the Ferryman to carry their soul across the River Styx and into the afterlife. Many other cultures have taken on some variation of this tradition — and they've persisted. Today, many people still leave coins on military headstones, and on the headstones of other dearly departed loved ones.
While it's not exclusively a military tradition, this is common at the resting places of fallen troops. But the thoughtfully placed coins can't just be left to pile up indefinitely — and the fallen don't have much use for them. Eventually, someone has to collect these coins and put them to good use.
So, what happens?
There's an often-shared chain email that suggests that the type of coins on military headstones impart different meanings — a sort of hidden message left to be interpreted by other veterans who visit the grave. A penny is used to simply honor the dead, a nickel means you went to boot camp or basic training with the fallen, a dime means you served with them in some capacity, and a quarter means you were there when they died.
This multi-coin theory is suspect at best. The first documentation of such a tradition is only as old as 2009, and you'll often find nickels, dimes, and quarters on gravestones from World War I and earlier — which just doesn't make physical sense. Still, this idea has been spread around enough that it carries at least some degree of significance.
When too many coins pile up at a gravesite, a caretaker collects the money and puts it in a separate fund to help pay for cemetery upkeep. The coins are put towards things like washing graves, mowing the lawn, and killing pesky weeds if the state or local government doesn't already allocate funds for such things.
The same fund also contributes toward the burial of an indigent veteran who cannot otherwise pay for the process. The VA and other charitable funds may help cover some of the costs, but if the veteran (or the veteran's estate) still cannot afford the difference, the coins left on the graves of their brothers- and sisters-in-arms will help.
While coins are most common — most people reading this article probably have a spare coin sitting in their pocket right now — other mementos are also placed on veterans' graves.
In nearly every case, caretakers will remove these tokens in order to keep the area in pristine condition. Rocks are also commonly used, but they'll more like likely be removed and placed nearby, for another visitor to "happen upon." Military challenge coins, however, are often left on the stone for years.