21 gun salute for the President

19 Gun Salute for the Vice President, Speaker, 5 Stat Generals/Admirals

17 Gun Salute for 4 Star Generals/Admirals

Here are two 4 star men you may know the names of:

Admiral Mike Rodgers (former head of the NSA, Trump Tower meeting on campaign spying)

General Paul Nakasone (current head of the NSA, quietly doing god knows what, scandal free, news media free, installed day one by Trump and still there)

I imagine Trump thanking Rodgers for bringing the campaign spying to his attention, that he deserves a 21 gun salute, and being corrected that 21 is reserved for a President, and for a four star Admiral it would be 17. Perhaps an inside joke that recurred between them that later lovingly spawned 'Q'

So when you see 17, the President might not just be hinting at us all, but may also be saluting Rodgers, if not both these two men for their (ongoing) service

Source:

For each flag rank junior to a five-star officer, two guns are subtracted (e.g., for a four-star admiral, a 17-gun salute is prescribed; a three-star general would rate a 15-gun salute; a two-star, 13 guns, and a one-star, 11 guns).