First, ensure that your local code is up to date and allows you to issue citations based on rubbish, neglect and deterioration that impacts other properties, consistent with the state's Minimum Livability Code. For examples of nuisance and other property maintenance ordinances, contact the MML Research Department
Update your definition of "vacancy." Many jurisdictions have a definition that hinges on whether the property is "unsafe" or "unfit for habitation." If so, consult with your municipal attorney and consider changing the terminology to "nuisance" or "uninhabited." Also, remember to take into consideration that people might be squatting in the property, so make sure that this is defined out of "uninhabited."
Finally, CITE, CITE, CITE. If you do not have citations on record, there is nothing to enforce. Add administrative fees to your citations and bring the owner or bank to court for non-payment of the administrative fees AND the citations. Remember, you can always waive the administrative fees later, but they will be useful in the short term to get the attention of the owner or bank and bring them into the discussion.
You can also place liens on the property based on the citations and fees. This will ensure that the town is made whole upon sale, and also place the town in a better bargaining position should you decide to pursue receivership.