To mark = To acknowledge or celebrate (an important event) with a particular action. It is not tragic. The event that is being acknowledged or remembered could be happy (a jubilee) or tragic (a war).
To mark would imply an action/event of remembrance or celebration that is of a certain scale. We would not say, "To mark his birthday, we had a drink in the local pub." We would say, "To mark the Queen's Diamond Jubilee, a service of thanksgiving was held at Westminster Abbey."