Pick the name of a unit:
"These are the Screaming Eagles out of Fort Campbell."
Or a battle:
"This is from some old friends of mine who fought in Vietnam."
Or a big title:
"MacDill, that's from the chief of staff down there."
And chances are, it, or that, or they, have a coin, and that Mark Van Trees has it, somewhere.
"It's something you can put your hand on, a token of those people that raise their hands, swore an oath to defend this country."
They're called 'challenge coins." They measure two inches across, are an eighth of an inch thick, weigh an ounce or two, and are minted mostly by private companies around the world.
"You're not going to find any two of those coins the same," Van Trees said. "Each one is different. Each one is designed. Each has their own personality."
If they exist, there's a good chance they're in his office.
"We had a retired Navy guy who made all the racks for them to display them all."
Van Trees is the proud owner of a collection that he never sought out.
He can say with certainty that he has never asked for a single one of these challenge coins.
"It is reserved as a thank you."
He and Bob Williams run Support the Troops, the Wesley Chapel non-profit that sends care packages to troops all over the world.
Troops have sent the coins as thanks, not realizing they were helping to build what Van Trees believes is one of the largest collections of challenge coins that isn't for sale.
"It just happened," said Van Trees. "Bob as you can see by all the certificates and stuff, Bob's first and foremost and only passion is taking care of as he called it, his kids, his troops, and it just kind of grew."
They haven't counted, but they believe they have 3,000.
"When you first come here, you first go, whoa," said Van Trees.
Like anything, there are rules and regulations. Ones concerning challenge coins are mostly unwritten -- one never asks for one.
But if you meet someone who served, you'll find out why they're called challenge coins.
"What you do is you keep it in the right hand and then you shake hands, and as you shake hands you squeeze, and you hand off the coin."
If you say you served, and don't have your unit's coin when challenged, you'd better have your wallet.
"If (you) didn't have (your) coins, you bought my drinks for the rest of the night," said Van Trees. "You always kept your coin with you."
Wikipedia says they first became popular during World War I after a medallion used for identification helped a prisoner escape German custody.
Van Trees has three coins on his desk that are most special.
"It means a lot when someone gives you a coin," said Van Trees. "You cherish it and you remember it."
Those coins are from the parents of fallen troops.
One of them is the coin of 24-year-old Dimitri del Castillo of Tampa.
"I look at them everyday," said Van Trees. "It reminds me that freedom isn't free."
Van Trees is surrounded by those reminders.
"For the last forty years we have put our kids all over the face of this earth protecting freedom. We are going to keep sending care packages," said Van Trees. "We are going to keep adding to the collection as we get more."