10:17 AM PT -- Turns out Alessandra's not the Halloween-Scrooge she appears to be ... we're told the pics show her in front of a friend's house in Santa Monica. She and her fam went there to visit and trick or treat -- but the sign was not her handiwork.
Alessandra Ambrosio apparently has an issue with trick or treaters showing up at her house -- because she literally told them to "f*** off."
Ya gotta see the signs the retired Victoria's Secret supermodel posted by her front door on Halloween -- one reads, "No Trick-Or-Treat Sorry :( " ... and the other drives the point home further, saying "AKA F*** OFF :) "
The handwritten notes are taped right next to the doorbell ... so ya couldn't miss it, and Alessandra's even standing guard outside, pointing trick or treaters in another direction.
It's unclear what Alessandra's beef is with candy-seeking kids, because she's not against Halloween or trick or treating at other folks' homes -- she and her man, Richard Lee, dressed up the family in "Squid Game" costumes and took her son door-to-door asking for candy.
So, this is more of a "do as I say, not as I do" vibe from AA.