Abstract: A method of forming a decoding device to enable hidden information or indicia on an article to be revealed is described. The method comprises electronically transferring data defining the decoding device from a central source (3) to a remote site (6). The decoding device is created at the remote site (6) using the transmitted data.

Abstract: A document of value such as a banknote comprises a substrate having a security feature in or on one region of the substrate. The security feature has at least one machine authenticatable high security entity (HSE) and at least one further machine authenticatable entity comprising a low security entity (LSE) or a high security entity, the at least two entites providing different detectable characteristics. The or each HSE is an homogeneous mixture of at least two components exhibiting different detectable characteristics, and the LSE is a single component exhibiting a detectable characteristic different from those exhibited by the HSE.

Abstract: Raman-active compounds such as polydiacetylenes are provided in the form of particles whose maximum dimension is 40 .mu.m. They can be formulated into inks, for the purpose of printing on security documents which are thus readily capable of authentication.

Abstract: This invention relates to documents, such as banknotes, which are produced and used in large numbers and which, for a given series, are identical one with another except for a unique multi-digit number upon each individual document, the number thus uniquely identifying that document within the series. According to the present invention, to render unauthorized reproduction of the document more difficult, on each document, at least two characters in the identifying number differ from each other (in addition to any differences in the letters or digits which they represent) in one or more visible characteristics. Thus the differing characters may have different heights or widths or be in different styles of type. Preferably, the identifying number appears twice on each document, in diagonally opposite corners, and preferably the variation of physical characteristics of the characters along the length of one of the numbers is reversed in direction in the other of the numbers.

Abstract: This invention relates to documents, such as banknotes, which are produced and used in large numbers and which, for a given series, are identical one with another except for a unique multi-digit number upon each individual document, the number thus uniquely identifying that document within the series. According to the present invention, to render unauthorized reproduction of the document more difficult, on each document, at least two characters in the identifying number differ from each other (in addition to any differences in the letters or digits which they represent) in one or more visible characteristics. Thus the differing characters may have different heights or widths or be in different styles of type. Preferably, the identifying number appears twice on each document; in diagonally opposite corners, and preferably the variation of physical characteristics of the characters along the length of one of the numbers is reversed in direction in the other of the numbers.