If you ever stumble across some U.S. Army correspondence, you're fairly likely to see this phrase or one like it. It will appear just before the signature at the bottom of the memo/letter/whatever you're reading and it will look cool as hell. As you may know, all military commanders are absurdly overburdened, and unless specifically required to write a piece of correspondence themselves, they will delegate the task to one of their many subordinates. This is what subordinates are for, and why commanders wanted to be commanders in the first place.

The rules-- there are rules, of course-- for such delegation are spelled out in excruciating detail in Army Regulation 25-50. This tome of a rulebook weighs in at 121 pages, which might not seem like much until you've seen the title: Preparing and Managing Correspondence. That's right, it's 121 pages of How To Write A Memo!

Section 6-2 (that's in the sixth chapter of How To Write A Memo, mind you) lays down the law on FOR THE COMMANDER usage:

f. Delegated to the subordinate. When a subordinate has signature authority, the subordinate will use an authority line to show for whom he or she is signing.
...
(2) FOR THE COMMANDER: Documents signed by the commander's staff normally use this authority line when the document pertains to command policy.

This happens so commonly that the "authority line" has been specified as the place for any such indications of delegated signature authority. You may also see "FOR THE COMMANDER IN CHIEF" or the like, or "BY ORDER OF ...". The latter indicates limited signature authority vested in the subordinate, presumably because all the trustworthy subordinates are busy drafting the next chapter of the rules on pants.

FOR THE COMMANDER:

--elephino