HOUSTON -- If you’ve spent time at a national cemetery, you may have noticed coins on some graves.

A lot of people are unfamiliar with the tradition, but it’s a way fellow veterans honor the fallen.

A penny means someone visited the grave to pay their respects.

Nickels say the visitor trained at boot camp with the fallen veteran.

A dime means the two served together in some capacity.

A quarter, which is the most rare, signifies the person who left the coin was there when the veteran was killed.

Mat Williams, director of the Houston National Cemetery, says veterans leave coins on graves year round.

“It’s admirable. They come out here and just let the family know their loved one hasn’t been forgotten. They’re visiting their fallen comrade,” said Williams.

Williams explained some veterans also see the tokens as a down payment to buy their comrade a drink in the afterlife.

He says rocks carry the same significance.

The Houston National Cemetery leaves coins on graves for as long as possible. However, if they fall off and no one collects them, the money goes towards a fund to beautify the cemetery.