What I have done with mine at a very early age is bring them around officers and firefighters in uniform. It has worked. They are very neutral to police. I have walked them past fire trucks, police cars and ambulances with lights on and sirens too. I also include landscapers working. I can cut my grass with them right in the yard without issue.
I did this for socialization purposes.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD