I just had a nice success and thought I'd share: for anyone who has ancestors who were on the New York City police force, you can send them a request for information.
I sent a request in for my great-grandfather's records at the end of March and by mid-July I received a nice cover letter, his "Force Index Card" and "Transfer and Assignment Card."
From those I learned some excellent information: His exact birth date, naturalization date, addresses, precincts, previous work before going on the force (he was a Hostler, or stableman), retirement date, death date, pension amount
If you send in a request I suggest you include as much information as you can - all I had was his name, a possible death year and his addresses from the 1900 and 1910 censuses.
I also suggest you send in a self-addressed, stamped envelope - while they did not use mine and send it back in a large envelope (postage was greater than $1.20 too), it is probably a good idea to do so.
Hooray for the NYPD!Address:
New York City Police Department
Personnel Resource Unit
1 Police Plaza Room 1014A
New York, NY 10018