Anyone that sees that decal in the clear light of day will know that
it's not real.
But, at night, with only street lights and your own car's headlights to
see by, it could look very real. It looks almost real in daylight.
I can see how that situation could lead to one angry driver to try to
force another angry driver off the road to help the helpless victim in
the back of his truck... ...especially if the first said angry driver
has a gun to protect himself from the second said angry driver.
But, if by chance that second said angry driver is also armed, we have
an extremely dangerous situation evolving out of a "joke".
Like I say, I think that decal belongs in the same bag as pointing a toy
gun at a cop. It could be the only funny decal in the world that could
get you killed. :D