Well, on one hand, if the owner complains of them loitering, they can be charged with trespassing. But only on complaint from the owner. The police can't make up trespassing charges for land that doesn't belong to them. They don't or shouldn't have a legitimate claim to create charges on people when they don't know if the people are trespassing. Absent complaint from the owner, the police have no authority to decide who is trespassing on who's land. Otherwise they will start charging home owners who are sitting on their own porch with trespassing. However, I could see there being a legitimate complaint from the owner as the owner may look at it as the room they are taking up hanging out there is room that paying customers could be using.