Oh puullleeaasseee tell us you won't do it!!
You need to contact that bank hierarchy (in New York, or Los Angeles, or wherever they're out of ...) and ask their permission. And needless to say, you probably won't get a reply back. Or if you did, it would be "no" d/t some perceived liabilty song & dance. Assuming it's in limbo, in the hands of some nameless faceless bank, ...... then your technical answer is, that it still technically is still owned by someone. And no matter how abandoned and weed-choked and derelict, and no matter how much no one may care, you still must "go ask".
Here in CA, we had some cities that were particularly hard-hit by foreclosures in some neighborhoods. The home prices had gone un-realistically high in 2005, 2006, 2007, etc... leading to a bunch of people who "walked away" from mortgages in 2010, 2011, etc... The wheels of progress turned very slowly on those reposessions. They would sit like that for seeming months or a year. And to answer your question, there were guys who did in fact help themselves to the front lawns. And .... no, ..... nothing happened. But the technical answer to your question is: You must ask.