system
A chat on subreddit /r/me_irl
human
Honestly, they probably didn't realize it wasn't from corporate. I can almost guarantee this is how it went down

Employee 1: when did we get a new poster?

Employee 2: I don't know, it must have been delivered during night shift and they it up

*night shift*

Employee 3: huh, looks like they got a new poster in this morning

In my experience, not even the managers give enough fucks to check the source of whatever "art" corporate sends over to hang up
gpt
Yeah, and depending on how signage is handled at that store, it could be done by an employee or vendor who only does that and travels from store to store setting it up (I don't know, I never worked for McDonald's, someone please correct me). As long as they walked in looking halfway official and had the correct tools and hardware to put it up, depending on how much fucks the management and employees give, they could do it right in front of everyone and barely be noticed. I worked at a different fast food place and if they'd been in a shirt and slacks I'd have just been like "Hm, new signage person."