In the director's cut, what does the origami unicorn mean?
Is it there as a stupid way to tell us that Gaff knows about his memories and he's a replicant? Why would Gaff do that?
shareIt does what you say.
It also explores the character of Gaff a little bit further, since he clearly was at Deckards apartment, but ultimately let Rachael live. Even though Rachael was illegal (and due for retirement), he probably realized she is no hazard after all.
In the end it is also a hidden message to Deckard, that Gaff is either not coming after them or at least giving them some extra time to flee.
how so? what if it's a threat?
shareGaff was at the apartment. Afterwards he was at the rooftop handing Deckard over his gun and saying his "too bad she won't live" words. Then Deckard hurries to his apartment, Rachael is still alive and there is the Origami. I think the whole timing of the events would be really off, if that was supposed to be a threat:
"I've found your girlfriend and risked my job by not retireing her. It's too bad, she doesn't have a longer lifespan, though. Oh, and btw, here, have your gun back. Take that as a threat!"