A subtrate, (1) e.g. of thermoplastic or paper material, has embossed thereon first (2a) and second (2b) non-light diffracting relief elements which define first and second patterns, respectively. The patterned area is uniformly reflective. For example, the first relief elements (2a) form a background area in which are arranged the second elements (2b) in the shape of a company logo. The first (2a) and second (2b) relief elements are so strutured that when the direction of view thereof is changed from a first to a second direction the relative perceived distinctness of the first and second patterns is changed. The substrate may form part of a security document whose au t hen- ticity may be checked by ensuring that the relative distinctness of-the two patterns changes with the angle of view.