Law enforcement officials investigating the blasts in Austin and Shertz, Texas say you should be on the lookout for anything out of the ordinary, including suspicious mail or packages.
If you find a suspicious letter or package, do not handle it or pick it up. Immediately clear the area of people and pets, and call authorities.
Here are nine signs a package might be dangerous:
Check the handwriting. Misspelled words, badly typed or written lettering, restrictive markings and no return address could indicate trouble.
Labels could be a red flag. If a package is sent with an incorrect title or addressed to a title only, it has the potential to be dangerous if opened.
How is the package shaped? If the package is lopsided, uneven, rigid or bulky in appearance, it may contain potential hazards inside.
SUSPICIOUS PACKAGES: Pay attention for these signs
Is there tape on the package? Postal officials say letters or packages sealed with excessive amounts or tape may be dangerous.
Stamps could be a clue. Foreign postmarks and excessive amounts of postage should be a red flag this package might contain something harmful.
Check for stains on the package. If you see stains, discoloration or crystallization on the wrapper, this could be evidence of a chemical or biological hazard inside.
Beware of foul odors. While postal officials said you should never open, smell or taste a suspicious package, the presence of odors out of the ordinary should be a clue of a dangerous parcel.
Check for wires protruding from the package. This could be evidence of a package bomb.
Is there powder inside? Envelopes containing an unknown powder have been reported throughout the United States, especially after the September 11, 2001 terrorist attacks in New York and Washington, D.C. If you receive a powdered envelope, call 911 and evacuate the area.
If you should receive a suspicious package at work, you should inform your boss or human resources department, and activate your workplace emergency plan.