WYD Logo

Via Amy Welborn's site, I found a link which explains the symbolism behind the World Youth Day Logo.
For starters:

The most important moment in the World Youth Day is the encounter with Christ, represented by the cross that dominates the Logo at its very centre. It is Christ's presence that characterises this event. The colour red symbolises the love, the passion and the pain. It indicates God's love and Jesus' death on the Cross, but reminds one of the pain present in our lives and all over the world. The cross is the main symbol of Christian hope and of redemption in Jesus Christ, which is greater than any pain.

For the rest of the explanation, go here.