I became interested in military death and calling cards when my brother was presented with an ace of spades from a retired door gunner. The gunner kept the card on his person during the Vietnam war. 30 years later, my brother Waylon was a door gunner from the same squadron (HCS-84). For him, it was a huge honor to be handed the card understanding who it came from and what it meant. It's now framed and proudly hangs on his wall at home.
As you noted, after 9/11 the world changed for us all. I'm a senior firefighter. I've started a tradition (by invitation only) with a few firefighters using the Ace of Spades Calling Card. I explain to those I give a card to that death will happen, to prepare for it, and fight against it. "Get ready--stay ready" is my motto. The card is taped inside the fire helmet as a reminder of what our purpose is "to save lives and protect property." For every fire death we have, the card gets a single mark--like a tally score. Every mark gives increases the sense of purpose. For guys with no marks yet, it's a reminder that their time is coming. It's a powerful reminder of purpose and calling every time we don the helmet.