Yup it happened to me.
At first I started having strong contractions (didn't think much of it since I've been having false labor for a while) Then i felt as if i needed to go to the bathroom. My stomach felt loose and I thought I was going to have diarrhea. In one of my trips to the bathroom I lost my plug. I was in labor! 4 hours later I was holding my little girl.
It can be a sign depending how far along you are! Some women get diarrhea instead of being constipated it's usually because of the higher water intake! But if you are near due than it can be a sign
I did with my 2nd and my dr said its a sign