I saw several people wearing ashes yesterday-- on the plane  back from Boston, running the cash register at Au Bon Pain, in a law office.  Seems to me that's a pretty-courageous act these days. 
First of all, when you do that you self-identify as a person of faith, someone who actually believes the Gospel message of Jesus  death and resurrection for our salvation.  In certain circles that marks you as someone who is a bit unsophisticated, backward, naive, perhaps even bigoted.  You get funny looks, and the subtext is always that you shouldn't push your religion in my face, so stop the outward display of faith.
But there's more going on than just the occassional disapproving look.  When we wear ashes we're communicating a message that is hard for our society to hear.  We're saying that we are sinners, and, by extension, that sin exists.  Fundamentally we're saying that there are attitudes, behaviors, actions that are wrong.
 We are affirming in public what Pope Francis said in one of his early interviews where he was asked to describe himself and, after a bit of a pause, said: "I am a sinner."  He emphasized he did not mean this in simply a metaphorical way, but that he sins personally, as we all do.
That's a tough message, especially these days, because it runs directly counter to the modern cultural norm which seeks to make all judgments about our behavior self-referential.  There aren't any higher rules or norms or standards, we're told.  What's right for me may seem wrong to you, and vice versa, but there's nothing beyond our own self-gratification to use as a standard.
Wearing ashes says that view isn't correct-- that there is more to moral judgments than our own perspective.
But the beauty of wearing ashes is that the ashes are placed on a person's forehead in the sign of the Cross (or at least someone tries to do that--- it's harder than you'd think).
The ashes aren't a sign of our condemnation, although they are a helpful reminder that we all have places where we sin, where we could live our lives with more love and charity and joy.
The ashes are a sign of our salvation, of God's unfailing mercy and love, and of the ultimate joy of Easter.
In a modern world that says it wants people to be happy, but then seems bent on making happiness impossible, maybe it is that aspect of the ashes-- the message of the joy of the Gospel-- that is most culturally challenging, and the one all of us most need to hear.