See my comment below. DO NOT CALL THEM BACK. Look up the real Verizon number on your bill and use that instead: these guys are NOT Verizon and if you give them your credit card number they won't just take the 20 bucks or whatever you think you're paying them.
I don't think it's actually a scam...I believe the Police Officers' organization is a legitimate nonprofit...but this one and AmVets are particularly annoying in their fundraising (I presume performed by a contract fundraising firm). I'm glad I didn't answer the phone!
All of the companies that are paid to raise money for charity are rip-offs. Typically the charity only gets 30% of your donation. The companies that call for donations for the police department are much worse. The police may get as little as 5% of your donation.
Don't donate to the callers. If you want to donate to a police charity call the non-emergency number for your local police deparment and ask them where to send a check.