With my third baby, I suddenly had a surge of energy a day or two before - I was cleaning like mad, going for walks, generally thinking ‘this is ok’. Then in the night the contractions started. That was the only time there were ‘signs’ that it may be happening soon.
With my first pregnancy, the early labour stage lasted a very long time (2/3 days), which wasn’t so bad. It started off as light cramping, that lasted for days and got worse towards established birth. Had slow release of waters over a day or so.
Second pregnancy included the typical ‘whoosh’ of breaking waters you see in films. He was a very bouncy foetus and he basically gave me a gigantic kick in the night and my waters broke!
Third pregnancy, my contractions started and my waters were in tact all the way until I was ready to push! Midwives broke my water to make the birth quicker.
Fourth pregnancy, and contractions started hard and fast, very painful with no warning. Turned out I had a massive baby and didn’t know it (9ib 10oz), so when she was born back to back it was a shock to see how big she was. I was in so much pain I went to the delivery suite early, and she came quite fast (for me).
I would say, there aren’t always signs, only the contractions starting.