Matthew 6:1 - “Beware of practicing your righteousness before men to be noticed by them; otherwise you have no reward with your Father who is in heaven.”
Ashes on one's forehead are hardly a mark of "righteousness" - they are a public admission that one is a sinner.
Please--I realize that many people misunderstand this practice but receiving the mark of the cross in ashes is NOT a sign of outward piety. Rather, it is a reminder of our mortality. Sin entered the world through one man and death through sin--each of us is DYING. But the mark we receive is in the form of the Cross--the LIFE-GIVING Cross.
Further, the practice is not unique to our Catholic brothers and sisters. As a Lutheran pastor, I can testify to the power of the words "Remember that you are dust and to dust you shall return." And even now I anticipate with joy the words of the Easter Vigil: "May the light of Christ, rising in glory, dispel the darkness of our hearts and minds."
As has already been noted, ashes reflect the exact opposite of righteousness. Gotta do a little reading up there, fella.
Ashes are not a sign of righteousness, rather the opposite - penance and humility.