It can be used as a singular or plural noun.
To avoid confusion, you can use the word 'policeman' to make it different. Usually, having an article will give you an idea of the number, but in this case, 'the police' can still be used as a plural noun. It would still be your preference and when you are going to talk or right about the police, you can use policeman for singular and police for plural.
I can't give a stand from a native speaker but I have friends who are native speakers and they agree with me on this point. I hope this would help you.