The Ash Wednesday Gospel speaks against disfiguring faces to show others that you are fasting. People sometimes mistakenly think that's what the ashes for which this day is named are all about. Wrong.
The ashes are put on with the words from Genesis 3: "Remember, O Man, that you are dust, and unto dust you shall return." The ashes show not fasting, but DYING. They are sign not of practicing piety, but of the rock bottom reality of life in a fallen world. They announce to us: "I am dying...and so are you."
But the ashes are always placed on in the form of a cross to remind us that there is a reality that is even more rock-bottom than death: there is One who became our dying Dust for us and took that Dust through death upon a cross and burial into a glorious resurrection and a life that never ends. We are dying; we are headed to death indeed, but we do so in faith in Him who shared our nature to make us divine, who became a child of man doomed to dust, that we might become the children of God, destined for heavenly glory in union with Him.