I am currently a Firefighter involved with the city's drone program. Together several entities(Police, Fire, Public Works, Risk Management, Business Administrator, Code Enforcement, Beach Patrol) of the city all took a local college class and then all obtained Part 107's. This was done to try to put all involved on the same page. I am currently the coordinator for the drone program on the Fire side and often interact with the Police side. When I asked some of the officers that are Part 107 and more knowledgeable on the rules how they would respond to any perceived illegal drone flights I was told this. Paraphrased: For the most part any contact would be mostly likely made from a complaint unless an offense was witnessed first hand by an officer. They try to follow this:
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Which is currently posted on FAA.gov
They will find out under what the person is flying (107, hobbyist), ask for proof of registration, look for registration on the drone, proof of 107 if its a commercial flight.
If it was a complaint (Peeping Tom, flying over critical infrastructure, flying over people) they may ask to view footage, and possibly confiscate the drone. They might not even need any information from the drone operator as cell phone video from the reporting party seems to be almost the new norm. We have beaches and the Beach patrol has a real problem with drones hovering over sunbathing women.
A lot of it is situational. If they see a drone fly across a busy roadway, yes they are going to take action. If they see a drone hovering over a sunbathing woman, they are going to take action. A lot is going to depend on the initial investigation where they question "detain" someone. A disorderly person charge is one of the most widely abused(one perspective), used (another perspective) charge that can also be used beside trespassing (yes if your drone is flying over critical infrastructure like the power plant) they may try to pursue this avenue. And at this time they have not had to charge anyone. Maybe charges they apply will not hold up if tested as a lot of this is new to them. Several police officers have a Part 107 and many have their own drones. They are not antidrone. But if calls are made by the general public, they must investigate, and yes drone owners are going to be angry just like when the police show up to investigate anything since most people do not like officer initiated encounters of any type. Drone enforcement for us is a low priority since most of the city has inner city problems, but if someone calls to complain or an officer sees unsafe or illegal drone usage, they are going to intervene.
In regards to the OP as someone else stated the full picture of this is not known. Did someone call to complain? Was the drone flying over people or hovering outside someones house. The person who called (If there was one) may just not like drones and may be ignorant in the laws regarding them or even exaggerated what the OP was doing. The police are going to have to investigate a complaint, they do not know if the caller is exaggerating or flat out lying unfortunately. And keep in mind as someone else stated trespassing laws are going to vary state to state.
OP I am sorry you had to have your property confiscated just to prove you were not doing anything illegal. Maybe everyone should be prepared for this situation, have all of your documentation on hand and even offer to show the police your flight logs and obtained data if that will expedite the encounter and perhaps not end with them taking weeks to confiscate your drone and look at all the data on it.