A tilak or tilaka is a mark made on the forehead and other parts of the body with ash, sandal paste, or kumkum. Different streams use different substances and shapes.
Within the International Nath Order the usual mark is three horizontal lines of vibhuti. In initiation that ash is also set on several parts of the body. The fire that makes the ash is the dhuni. Tilak is the mark. Vibhuti is the ash. This is not a costume and not a chart of every Hindu sect.