Here is how the military defines D-Day.
>In this case, the “D” in D-Day doesn’t actually stand for anything—it’s merely an alliterative placeholder used to designate a particular day on the calendar.
Pic is interesting.. if we see a numerical marker then maybe that will tell us D-Day is x # of days away.
https://www.history.com/news/why-was-it-called-d-day
We have been seeing lots of D5 markers from Q, so perhaps today from Q+ signified that D-Day is 5 days from today. Also known as Christmas Eve.
12/21 is also the deadline for the voter interference EO that took effect after the midterm elections.
It's also related to the picture POTUS tweeted with the caption "SANCTIONS ARE COMING" in GoT font because the line from GoT is "WINTER is coming". 12/21 is the official start of WINTER, and quite possibly, SANCTIONS.