This is a perennial thread, although it hasn't come up lately.

1. Leave a note on the bikes just in case they are in use. If they are, you've got no beef.
2. If no one responds to your note, find out who owns the rack and let them know about the situation.
3. If they're not inclined to take action, ask them what their policy is on abandoned property, and whether that would allow you to cut the bikes off the rack and give them to a local bike co-op.