You can only receive tag badges for tags which are used on 100 or more questions. Modulation from D major to D minor, should I go sudden or gradual? was the 100th such question, asked two days ago, and this event made the [modulation] tag eligible for tag badges. Those are usually awarded somewhere in the early UTC morning, that job runs once a day.

Only top voted, non community-wiki answers of a minimum length are eligible