A BG seeing such bumper stickers might follow me to my house, then wait for the right opportunity to break in, on the reasonable assumption that I have guns in the house.
That was written by someone who pontificates too much.
Sure, anything could happen, but is it reasonably likely to happen? Of course not. I think it's just as (un)likely that a BG would see the stickers, follow me to my house, note my address, and pass slong to his BG friends that they don't want to mess with the residents at that address because we are almost certainly armed. Both scenarios are equally highly unlikely.
Burglars are among the lowest of the criminal food chain and, with the exception of the high dollar heist specialty burglars (more common on TV than in real life), are almost exclusively drug addicts who act on opportunity above all else.
A truck plastered with gun stickers might make a burglar think there is a gun in the truck when it's in the mall parking lot, but it might also make him want to steer clear of that vehicle on the chance that it's owner could return and be armed.
Leaving that cell phone, laptop, leather coat, purse, iPod, etc... on the seat is much more likely to cause you to be a victim of burglars than any bumper sticker.