A skull and crossbones is a symbol

Symbol

A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

 consisting of a human skull

Human skull

The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

 and two long bone

Long bone

The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities and they are crucial for skeletal mobility. They grow...

s crossed together under the skull. It is generally used as a warning of danger, usually in regard to poison

Poison

In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....

ous substances, such as deadly chemicals.

History of the symbol

Actual skulls and bones were long used to mark the entrances to Spanish

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 cemeteries (campo santo). The practice, dating back many centuries, led to the symbol eventually becoming associated with the concept of death

Death

Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

.

In 1829, New York State

New York

New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

 required the labeling of all containers of poisonous substances. The skull and crossbones symbol appears to have been used for that purpose since the 1850s. Previously a variety of motifs had been used, including the Danish

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

 "+ + +" and drawings of skeleton

Skeleton

The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...

s.

In the 1870s poison manufacturers around the world began using bright cobalt

Cobalt glass

Cobalt glass is a deep blue colored glass prepared by adding cobalt compounds to the molten glass. It is appreciated for its attractive color. It is also used as an optical filter in flame tests to filter out the yellow flame caused by the contamination of sodium, and expand the ability to see...

 bottles with a variety of raised bumps and designs (to enable easy recognition in the dark) to indicate poison, but by the 1880s the skull and cross bones had become ubiquitous, and the brightly coloured bottles lost their association.

Modern uses

Today, the skull and crossbones is still the only standard symbol for poison. It is, however, less common outside industrial usage than it once was. Apart from its negative marketing effect on environmentally conscious consumers, it may actually attract children due to its association with pirates

Piracy

Piracy is an act of robbery or criminal violence at sea. The term can include acts committed on land, in the air, or in other major bodies of water or on a shore. It does not normally include crimes committed against persons traveling on the same vessel as the perpetrator...

, a popular toy and play theme. For this reason, in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 there has been a proposal to replace the skull and crossbones by the "Mr. Yuk

Mr. Yuk

Mr. Yuk is a trademarked graphic image, created by the Children's Hospital of Pittsburgh, and widely employed in the United States in labeling of substances that are poisonous if ingested.-Overview:...

" symbol. However,
Mr. Yuk and his graphic rendering are registered trademark

Trademark

A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

s and service marks

Service mark

A service mark or servicemark is a trademark used in some countries, notably the United States, to identify a service rather than a product. When a service mark is federally registered, the standard registration symbol ® or "Reg U.S. Pat & TM Off" may be used...

 of his creator, the Children's Hospital of Pittsburgh of UPMC

Children's Hospital of Pittsburgh of UPMC

Children's Hospital of Pittsburgh of UPMC, a hospital of the University of Pittsburgh Medical Center, is the only hospital in southwestern Pennsylvania dedicated solely to the care of infants, children and young adults. Care is provided by more than 700 board-certified pediatricians and pediatric...

, and the rendering itself is additionally protected by copyright. This means that the name and graphic image cannot be used without a license from the owner—unlike the Skull and crossbones, which is in the public domain

Public domain

Works are in the public domain if the intellectual property rights have expired, if the intellectual property rights are forfeited, or if they are not covered by intellectual property rights at all...

.

Unicode

Unicode

Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

uses for the symbol.