I recall there was some understanding that it had a legitimate use as well as the obvious marketing, which was to advise the reader that the message may be unexpectedly concise or contain errors because it was sent from a cell phone, something less common before the iPhone came out. BlackBerry phones did this too for the same reasons.

You misunderstand the purpose of "Sent from my iPhone" - it was a status symbol, it showed that the sender was part of the superior iPhone owning elite. It was trivial to remove, but most didnt "oh, I am too busy too remove it, I guess I'll just leave it and let everybody know I can afford an iPhone".

You are right, it was advertising, but it advertized the user, not Apple.

At least “Sent from my iPhone” was a factual claim, unlike this mess.

“Sent from my iPhone” is a default signature, but you can change the message under Settings -> Apps -> Mail -> Signature (at the bottom of the options page)

These are the same thing. Marketing, and the ability to track reach. There's no other reason to do this.

As I've written elsewhere in the thread, having worked at a large Enterprise in collaboration with Legal, if there isn't tracking of what AI contributions you have, it's harder to be protected legally by ie Microsoft's indemnity clause if you're sued

It's definitely helpful to know whether a PR was AI-assisted or not and the git attribution line is a simple and effective way of communicating that.

I also recommend specifying model name and version so the maintainer knows upfront the level of slop they are dealing with.