Switch on outside of cop car?

[roundhouse]

Looks like the locking hub on my old Bronco

 

[Shemp]

Looks like a port to me.

 

[BIKER13]

Its a video blocker.You open it and take out a huge lead pipe and beat the **** out of someone video taping.

 

[07JKX]

It could be an autobot from Transformers. Id be careful

more likely a decepticon...

 

[Barton72]

Flesh light port.

 

[Kyzrsoze]

The city uses a lot of propane fueled vehicles. I'm betting that this is a secondary fuel cap.

 

[Kyzrsoze]

Here's your answer - just found this:

http://www.fleetsandfuels.com/fuels/propane/2012/08/sandy-springs-police-save-with-propane/

 

[TCW50]

Doughnut depository?

 

[PA4476]

Here's your answer - just found this:

http://www.fleetsandfuels.com/fuels/propane/2012/08/sandy-springs-police-save-with-propane/

Very good detective work there Kyzrsoze.

 

[payneed]

Here's your answer - just found this:

http://www.fleetsandfuels.com/fuels/propane/2012/08/sandy-springs-police-save-with-propane/

Wow, I'm impressed! The internet can be educational after all!
(my next guess was that the patrol car took a "hit" from a stray round of .22 and they drilled out and plugged the hole to prevent rust? Govt. efficiency (oxymoron) and all...)