Ashes on - or off?

Ash Wednesday is this week, and I have a question: Ashes on or off? That is, after leaving the Mass, should one wipe the ashes off the forehead or leave them on until they wear off naturally? I ask, because I am definitely in the “wipe them off” school, but would welcome the opinion and instruction of others.

For me, leaving them on would lead to the sin of pride: “Hey everyone, look at me – I have ashes on my forehead! Aren’t I pious? I am so much better than you because I go to church and fast and stuff.” As they say, it’s hard to look up and see God if you’re always looking down on others. I am reminded of how much Christ loathed the Pharisees and Sadducees and their outward, hypocritical signs of piety. Matthew 16 speaks, for example, to fasting like this:

And when you fast, be not as the hypocrites, sad. For they disfigure their faces, that they may appear unto men to fast. Amen I say to you, they have received their reward. But thou, when thou fastest anoint thy head, and wash thy face; That thou appear not to men to fast, but to thy Father who is in secret: and thy Father who seeth in secret, will repay thee.

Others, though, see the wearing of ashes as a public affirmation of faith, symbolic of the spirit of contrition. So I'll turn it over to others: What say you?