It’s a guess.
It goes with a Q reference to ‘On Guard’, which appeared near D5.
There is an old school of chess player that will say ‘On Guard’ when the Queen is threatened.
You may as well say ‘Check’, because typically there are only two times you threaten the Queen:
1. You put a Queen in a ‘fork’ (one piece threatens two big pieces at the same time). They generally have to move the Queen to save it, but they lose a Bishop or a Knight, say.
2. You’re about to put someone in checkmate, and you’re moving their Queen out of position.
‘On Guard’ then D5 could mean ‘We control the board, and are ready for endgame’.
Seems reasonable to me.
I really like that account of the “old school” player terms.
I believe the D5 on the board is also compatible to our president who himself has plenty of “old school” strategies to work his own board. Q would like your assessment. So would Trump.
Thank you for that excellent explanation.