Tester-Developer communication

Question

While a lot is written about developer-developer, developer-client, developer-team manager communications, I couldn't find any text which gives guidelines about tester-developer communication and relation.

Whether testers and developers are separate teams or in the same one (in my case, I am a lone tester in an agile development project), I have the belief that how testers are perceived is extremely important in order for testing to be well-accepted, and to serve its goal in enhancing the quality of the project (for example, they should not be viewed as a police force).

Any advices, or studies about how a tester should communicate with developers?

Update: Thank you all for your answers. They all confirmed what I had in mind. As for now, my team was very receptive of my role and we ended up making real progress. I could have chosen more than one as the answer but I had to make my decision.