There were certainly clues. As noted above, even in the theater release and "The Final Cut" there is the origami unicorn left at his house by police officer which indicates he knows what Decker has been dreaming of. In the Director's cut is was made even more obvious - In the scene where Decker looks in the mirror there is an electric glow which flashes in his eyes and in the scene where Roy Batty grabs Decker to keep him from falling to his death he mutters "kinship" as he lifts him to the roof. These last two items were deleted from the Final Cut to leave it more ambiguous.
In the scene where Decker looks in the mirror there is an electric glow which flashes in his eyes....
I don’t doubt they put that scene in there. But, IMHO, was a dumb move because it does not track with the rest of the story.