In Denmark, every year or two someone will put a tag around all the bicycles parked somewhere overnight. After a month or so, the still-tagged bicycles will be removed.

The local council do this in public areas, and the owners of buildings etc for private areas.

Really? Bikes are expensive in the US.

Only expensive bikes are expensive, you can pick up a cheap bike from Walmart for ~$100, or a used bike for less than that.

When a tank of gas costs $50 or more, $100 for a bike is cheap even if you have to replace it every couple months.