I'm not sure laying down is much of a sign, but this is what I've heard/what I've had one of mine do before she layed. Very red combs, hearing the egg song (Which is a loud bok bok BAGAWK) having a hen throw shavings/hay/bedding on their back, making practice nests, and doing the egg squat. The egg squat was probably the most noticeable for me. An egg squat is when a hen crouches and spreads out her wings, she will often fluff up and shake once you back off. This isn't a sign of laying, more like a sign the hen just reached sexual maturity and is acknowledging the rooster (You). But eggs follow soon when a hen starts the squat, same as the egg song.