It seems to me that most crime guns are reported as being "stolen" for their method of entering the illegal arms stream, people would want to take better care of their assault rifles. On the other hand, they are great for shooting kindergardners and cinema goers and not much else.
So, why not leave it in your car, especially if you are a pro-gun activist. We need more headlines like this one from the Salt Lake Tribune:
I have a post in the making called "why the pro-gun position may not be so good if you really like guns" and this might be a good thing to add to it.