Signature

The signature on a painting or other work of art has always been an important item in the assessment of art. Fake signatures are sometimes added to enhance the value of a painting, or are added to a fake painting to support its authenticity. A notorious case was the signature of Johannes Vermeer on the fake "Supper at Emmaus" made by the art-forger Han van Meegeren.

However, that oftentimes painters' signatures vary over time (particularly in the modern and contemporary periods) might complicate the issue. The signatures of some painters take on an artistic form that may be of less value in determining forgeries. For example, Daniel C. Boyer's gouaches are known for their often large, elaborate to the point of near-illegibility and multicoloured signatures.

The term "signature" is also used to mean the characteristics that give an object, or a piece of information, its identity—for example, the shape of a Coca-Cola bottle.

By analogy, the word "signature" may be used to refer to the characteristic expression of a process or thing. For example, the climate phenomenon known as ENSO or El Niño has characteristic modes in different ocean basins which are often referred to as the "signature" of ENSO.