severe cramping, red blood, loss of pregnancy symptoms
sometimes with a blighted ovum you don't know until you get an ultra sound
Large dark red blood clots, soaking through a pad an hour, severe cramping
Sometimes there are no signs that a miscarriage has accured. This happened to me with my first pregnancy. I thought everything was going well, went in for my 12 week scan and there was no heartbeat. I lost the baby just before 10 weeks. It's called a missed miscarriage.
My sister had a missed miscarriage. She had absolutely no signs. We went in and igoing out that the baby had stopped growing and had no heartbeat, but her body just wouldn't let it go for some reason.