A friendly face, an invitation to pray for peace, to find a moment of quiet, to experience a moment of grace, perhaps an encounter with Jesus.
Light a candle, come in, take some time in prayer or reflection, listen to music. (One element I noticed also at a church in Paris: times when priests are available for confession or just conversation. The Parisian church also had lay ministers available for conversation. I think both are helpful. Sometimes people want to talk to a priest. Sometimes people want to talk but not to a priest.)
I like this Night Fever idea. The article calls it a very subtle evangelization, one that takes away all the negatives. More than that, I think it is a ministry of presence. Churches and their communities can seem like another world when you are on the outside.
Even amidst the frenetic activity of the urban environment, the inner spiritual life is ever-present. It is easy to get caught up in the activity of the world and it takes discipline to quiet the mind and hear what is in the heart. This gesture–invitation, candlelight, music, presence–is a bridge that uses the senses to draw us from outside in so we can go out again a little more whole than we came in.