Here are the tell-tale signs to help you detect a suspicious package

(CNN) Bombs and chemicals sent through the mail are rare but terrifying. According to the US Postal Inspection Service, the postal service processes more than 170 billion pieces of mail every year and only a tiny fraction of those -- 16 over the last few years -- were investigated as mail bombs, says the US Postal Inspection Service. That, according to the agency, works out to be an average of less than 1 in 10 billion.

However, mail bombs can still be deadly, as in the package that killed a 17-year-old in Austin, Texas, earlier this year, or the Anthrax attacks in 2001.

Here's what postal services and government agencies look for when determining whether a package is suspicious:

What you should look for

Suspicious packages usually have several tell-tale signs, say investigators, security personnel and mail inspectors. The packages sent to the CNN offices in New York City and to several public figures exhibited many of them:

• The paper envelope was wrinkled and damaged
• Names and places on the sender's address label was misspelled
• One corner of the package was covered in stamps

What you should do

If you come across a suspicious package, here are some tips for what to do next, according to the Department of Homeland Security.

• Leave the package alone, clear the area and contact emergency personnel
• Wash your hands and other exposed skin with soap and water
• Cordon off the immediate area, and shut down all equipment there
• If possible, and without disturbing the mail, jot down what you can about the package (what it looks like, markings, the name and address on it)