I haven’t read all the responses, but Ingress have been around long enough for many officers to know what it is. Trust me, the Ingress community have had their contact with the police. They’ve done so with open arms and broad smiles.

So much so that some officers started playing Ingress themselves.

So just tell the officers that you’re playing a game similar to Ingress. They’ll probably just tell you to stay off private property and take care of yourself.