Is the cessation of bleeding sufficient for ghusl (ritual bathing), or is it necessary to see the sign of purity even if it is not observed?

If blood and the accompanying yellow or brownish discharge continue for more than fifteen days, then you are a woman experiencing irregular bleeding (mustahadah). If you do not have a regular menstrual cycle, then act based on differentiation (tamyiz): consider whatever has the characteristics of menstrual blood as menstruation, and anything else as irregular bleeding. The madhhab (definition) (school of thought) of Shaykh al-Islam is that yellow and brownish discharge are not considered menstruation at all. So, if the bleeding stops and the woman sees yellow discharge, she should perform ghusl (definition) (ritual purification bath) and pray. There is no harm in adopting this opinion if it is easier for you, especially if you are afflicted with obsessive doubts (waswasah).