I'm not anti-police, but I am a fan of knowing my rights when having an encounter with po-po! Keep in-mind this article focuses on Terry stops, & there's a BIG difference between that & popo observing us trespassing... http://www.policeo...se-stop-and-frisk/
If you're basically busted, being respectful & cooperative can go a long way, though you should be careful to not actually confess knowingly committing a crime.
On the other hand, stating "Officer, am I being detained?" before saying *anything* else can be even better, assuming you calmly walk-away without making any statements if the answer to your question is "no."