Abstract: An authenticatable item and security device carry a number of symbols (4A, 4B, 4C, 6A, 6B, 6C) identifiable to the naked eye, there being at least two sets of at least three symbols. All the symbols within a set are substantially identical, are positioned in a non-overlapping, regular geometric arrangement, and at least one common viewing angle of inclination, exhibit substantially the same optical performance, the optical performance varying with inclination viewing angle.

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: In a method of detecting sheets which do not have a genuine watermark (i.e. watermarks which result from variations in fibre distribution introduced during manufacture) the absorption of ultra-violet radiation is measured for each sheet in the area in which the watermark is expected to be present, and the transmittance of light by this area of the sheet is also measured. Sheets for which the absorption measurement does not show a substantially constant value, and sheets for which the light-transmittance shows a substantially constant value over the said area, are rejected. The absorption measurement is preferably effected by measuring the reflectance of ultra-violet radiation by the sheet, but the transmittance of ultra-violet radiation or the fluorescence of the sheet in the presence of ultra-violet radiation can also be measured. The measured value for the area can be compared with a reference value obtained by a measurement of the same parameter outside the watermark area.

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.