You can report abandoned bikes on public property via the city’s Report-a-Problem form.
If it is a private rack, contact the property owner or management company.
If the bike is parked on the UW campus, email their bike/ped coordinator.
Madison has a zoning code ordinance that details how much bike parking needs to be included with new construction and what kind of bike parking meets the requirements. This ordinance does not apply to already constructed buildings, but businesses or property owners may respond to a friendly ask for bike parking anyway. See above, “A place I am biking to doesn’t have bike parking.”
Reach out to the business and tell them about the City’s program to have bike parking installed. https://www.cityofmadison.com/bikeMadison/programs/bikeParking.cfm
For more details and email templates you can use, read this blog post.