Heavy bleeding and clots. I started spotting brown than a month later I was spotting again and found it stopped growing. Than a week later I passed it and bleed so much.
That is a tough question to answer because much depends on the circumstances. Very early miscarriages often occur, even before a women may know she is pregnant. They are often mistaken for a very heavy and often late period. In this situation, the only way to know for certain is if you knew you were pregnant and a Dr. following your beta/hcg levels. Even early u/s often won't show anything at this stage.
If you know you are pregnant and are further along, miscarriage symptoms are bleeding and cramping. However, many women will bleed in early pregnancy, even passing small clots. So again, the only way to know is diagnoses, usually through ultrasound.
If you suspect you are miscarrying, or have had a miscarriage, you should see your Dr. or if you are bleeding more then a maxi pad an hour, you need to seek emergency medical treatment.