I've been summoned 3 times as well, but instead of showing up to a note on the door, we were told to call a number after 6PM the night before to see if we had to show up. The number ended up going to a long list of names of people who did not have to attend. All 3 times my name was on that list, eventually.

There are some reasons why a cop would not use both lights and sirens. Sometimes it is best for them to only use one of their two ways of alerting others.

The only thing I could think of quickly is if they were responding to a crie in progress, such as a burglary or break in, where it may be beneficial to approach with as few things as possible giving you away early. In the situations I listed, an officer may be best to use only the lights for intersections only; I can't think of any reason to use siren only. Different types of calls need different responses.

I agree though, without lights and/or sirens, there should be reasons given for some actions.