I noticed a big personality shift in all my girls, around 19-20 weeks they got a lot friendlier, all of them started squatting for me (as the others have described) soon before they started laying. I had a couple of Easter Eggers that were terrified of me and would freak out if I even looked at them, they suddenly calmed down and started letting me handle them around the time of the first egg.
Their voices also seemed to evolve quite a bit, I started hearing the classic chicken sounds (bok-bok-bok, egg song, etc) around the time they started laying.