The item does not have to be delivered by a carrier; most bombers set up and deliver the bomb themselves. If delivered by carrier, inspect for lumps, bulges, or protrusions, without applying pressure. If it is delivered by carrier, balance check if lopsided or heavy sided. Handwritten addresses or labels from companies are improper. Check to see if the company exists and if they sent a package or letter.
Packages wrapped in string are automatically suspicious, as modern packaging materials have eliminated the need for twine or string. Excess postage on small packages or letters indicates that the object was not weighed by the Post Office. No postage or non-canceled postage is suspicious. Any foreign writing, addresses, or postage. Handwritten notes, such as: "To Be Opened in the Privacy of", "CONFIDENTIAL", etc improper spelling of common names, places, or titles, and generic or incorrect titles.
Check for leaks, stains, or protruding wires, string, tape, etc. If it is hand delivered or dropped off for a friend packages or letters, if there is no return address or nonsensical return address. Any letters or packages arriving before or after a phone call from an unknown person asking if the item was received are also suspicious