D5

D / sun (vitamin D, sunny D, etc)

5 / levels of solar flares 'A, B, C, M, X' Highest, or 5th level being an X class

so, D5 could mean X class solar flare

That said, here are just a FEW Q posts that make one have to wonder if this is in fact the case.

Search keywords on QMAP:

'Archive'- (X class would knock out electronics, we are advised a LOT to archive OFFLINE...PRINT IT UP)

'Sky'- (A sky event to occur, sky is falling week, etc)

'Light'- (lights going out, dark to light, etc. a ton of info...)

'EMP'- (risk of EMP from space)

'Dark'- (10 days of darkness, dark to light, spartans in darkness, BOOM gun ammunition)

'Blackout'- (The boom gun says blackout necessary, PG&E shutting off power in CA this week, Comms and media blackouts)

Theres likely more as well.

Maybe im digging too deep. The NPC's and shills will let me know the level of altitude I am flying at.