Aside from obvious markers like birthdays, which dates remind you of loved ones you've lost?
Because he was a World War II vet, Pearl Harbor Day reminds me of my Dad. Living through 9/11 has deepened my appreciation of the need for bearing witness. If my Dad were still alive he would be doing exactly that today; he was 23 years old on 12/7/41, the same age my daughter is now.
In addition, for reasons not wholly clear to me, my patriotism seems to be on the rise lately. My Dad was a patriot in the best sense of the word. Earlier today, taking note of the date, I felt Dad nearby.