It is a federal offense and enforced by the FTC

Can this lien be enforced on me, the new property owner?  

For apartments, you will have expenses not found with SFH's, such as snow plowing, grass mowing, possibly master meter utilities, cable TV, internet, common area lighting, trash dumpster, etc.You might also be expected to provide security cameras, mitigate parking disputes and enforce quiet hours.I would want copies of all leases, not just a "sample" copy. 

Laws like these generally have very little in the way of enforcement, because as you've discovered nothing in the purchase process will actually stop the sale except someone not closing because of the law.

I am not sure how they would enforce this on properties not in the PHA program?  

It is, so are probates, foreclosures, code enforcements, tax liens.

But apparently they do enforce these rules and if I ever wanted to move, I'd have to shut down that operation.Fun fact though, my next door neighbor is an STR house because it was grandfathered in.

My neighbors called the city code enforcement officer stating I am running a commercial business out of my home.

I won’t write much publicly, @Alexis Stevens, but happy to communicate offline or even over the phone if you send a PM to my inbox.In my experience, law enforcement will not investigate, so the main purpose of reporting is to protect yourself in case someone comes after you for committing a crime.

Yes @Emma Hans is exactly right and it sounds like you already know; Ithaca is bizarrely specific when it comes to code enforcement, historic preservation, and a bunch of other things that seem to make little sense.