Topics are closed for a reason and are handled very well by the Community Team. If you don't think they're doing their job, feel free to report it to Management. Now onto your question
Downloading:
First off, you'll want to download SparkIV here.
After you have downloaded the software, you'll need to find a decent looking Washington State Patrol skin on the internet. I've taken the time to find you one on our very forums, here.
Following that, you will need to find a suitable Crown Victoria (Or anything else) model to fit with the skin. I've chosen the following one for demonstration purposes.
Software usage and installation:
Now you're set to actually apply the skin. First off, extract SparkIV into a folder, and open it.
Then, you will need to click the GTA IV icon on the top left, leading you to its directory view.
Scroll down to the bottom and navigate to models\cdimages and double-click the vehicles.img.
Then, once you're inside the img file, navigate to your top tool bar and select the "Import" button.
If you haven't already, extract the vehicle from its RAR and import the file named "Police" or "Police2", and click Import.
After you have imported the files, scroll down until you find the imported file. You need to click on it once, and then navigate to the tool bar and click "Edit"
Once you're inside Edit Mode for the vehicle, find the following: police_sign_1, police_sign_2, police_sign_3, and police_sign_4.(They may also be named other things such as cvpi_sign_1. As long as it has sign_number, it's the one you want.)
Select police_sign_1 and navigate to the toolbar selecting "Import Texture" and import the Washington State Patrol skin you downloaded before. You will have to repeat the same process of importing for the other 3 police_sign's.
If you still need assistance, refer to the following video, here. (Credits to marc235786)
If you have any further questions, feel free to ask.
