As Desert Fox said.
I've been participating in digging IEDs out of the sand in Afghanistan. Of course that's a different ballgame than domestic US / Canada, but I'm used to treating suspicious objects with caution until their true nature is ascertained.
If it looks like a threat, the only thing you lose in treating it like one, is time.
On the opposite scale, if something is a threat and you don't treat it like one... either it's your own life, or your colleagues' at stake.