To whom is a coin valuable?

"Oh my..!"
"What's wrong, mom?"
"Oh, honey, I just.."
"Mom, don't cry. What's wrong?"
The silver-haired lady grasped her fist to her heart, sobbing silently. "Nothing is wrong, honey." She smiled after a few moments, her eyes still shining.
"Then why are you crying?" The young man held his mother tightly.
"I just found something I thought I had lost years ago." Tears started gathering and falling down her cheeks again.
"What is it?"
She opened her clenched hand and held what she had found up.
"You were worried about that?" He asked, incredulous. He picked up and studied the object. "Looks like just any beat up, old coin to me. It's not worth anything, mom. Even has a hole in it."
"It is priceless, honey." She took his hand and lead him to the closet and took down a photo album. Dusting it off, she sat on the couch and opened it, waiting until her son sat beside her.
"This coin is Vietnamese." She explained. "It was given to me in 1971. By your father." She looked down at the photos.
The young man recognized a few of the men in the photos. One was his dad's best friend. Another was a preacher from church. All had two things in common.
They all stood in the jungle and they all knew his dad.
"Your father sent this coin to me just after he got there. He drilled a hole in it so that when he came home and gave me his dog tags I could put the coin on the chain."
"Why would he give you his tags?"
"To show that he'd never go away again. When he came home we were going to marry." She smiled.
"But the day after I got his letter with the coin, I received this in the mail." She pulled out a letter with an official seal on the front of the envelope.
It was a death notice for his father.
"I was heart broken." She whispered.
He looked back at his mother. She was crying again. He wrapped his arms around her.
"Sweetheart, are you alright?"
The young man and his mother turned to the door and to the man standing there.
The lady smiled and here eyes lit again. "Yes, love, I'm fine."
"Hey, Dad, we were just looking at your old pictures."
"Is that what you're so worked up about?"
"Actually, love, I'm worked up about this." And she held up the coin.
"Wow... Where did you find this?" He asked quietly, gently. "I haven't seen it in years."
She chuckled. "In your old fatigue pants."
He looked to her, confused. "But how..?" And then his face lit in understanding.
"From the day I came home. You dropped it by accident and I had to grab it before we lost it. If I remember right, you dropped it because it was the first time you kissed me."