My company rents a building that is part of a complex built by a provider of electrical power. I worked as a consultant for said provider, so I know that one of the four buildings in the complex contains the personnel and the equipment they use to release electricity onto the grid and to monitor same. So, they are sort of sensitive about those buildings.
A suspicious package is any package left unclaimed for even a couple of minutes in a public area. I've watched the bomb squad hustle the packages out of the building into the courtyard more than once. I always send all my personnel to the other side of the building. At least if a bomb goes off they are not sitting in a room full of glass on the blast side.
I know, I'm just being a wiseacre! I find it silly that they tell us conststentlty to be on the lookout of 'suspicious' stuff, without much being said as to exactly what we are supposed to be looking for, that's all.
Now, that would be a novel way for getting rid of Aunt Martha's Christmas fruit cake ;-)
In my military career, nothing was not suspicious. If it didnt belong there and noone in the area claimed it, we called the Security Forces, no questions asked.
Now I work in a high rise building and people leave boxes and packages all over the damn place. I guess a bomb is gonna have to go off somewhere to bring the point home that packages and boxes sitting around are a security risk. It drives me nuts and I keep looking to see who is putting them out there.
Caviat, I was also a security officer in a classified facility for the last 3 years of my career, so maybe I am a little more paranoid than your average bear.