It's could very likely be a telemarketer seeking donations for a Fraternial Order of Police organization or similar; such fundraisers are mostly scams.

Another possibility is it's a prankster forging the caller-id ... very easy to do ... there's even is (or at least was) a website that will assist one in placing a call to someone using fake caller id; such services won't work for 911 nor toll-free numbers, since those use ANI which can't be blocked with *67 nor easily forged.

Some possibilities to consider.

Ron