Well, at some point this afternoon, I must have unconsciously rubbed my forehead. The guy who sits across from me just pointed that out. I went to the bathroom, and sure enough, my black ash cross was now a gray streak of dirt across the left side of my head.
I was annoyed at this, and mentioned to my coworker how I had wanted to preserve this ash cross through the rest of the day. He asked me why that was so important to me, and as I answered him, I realized that it wasn't a matter of penance, it was a matter of pride. The ash cross was supposed to be a mark of humility and repentance, and here I was trying to show it off, treating it like carefully applied stage makeup.
I was humbled by that thought, and will try to spend this evening focusing on the real purpose of Lent; a time to prostrate ourselves before God with a penitent and contrite heart.