1. In combination with a data source supplying a stream of binary signals defining both the identities of alphanumeric characters occurring in an ordered sequence and the position of each such character within a character group, an apparatus for detecting the occurrence of a particularly ordered group of R characters, said apparatus comprising: search memory means comprised of a first group of R sets of S bit storage devices wherein R represents the number of entries in a character position field and S represents the number of entries in a character identification field, each of said bit storage devices defining a first or second state; first means responsive to the position within a character group of each character defined by said binary signals for addressing the corresponding one of said R sets; second means responsive to the identity of each character defined by said binary signals for addressing the corresponding one of said S bit storage devices within said addressed one of said R sets; and third means responsive to said first and second means addressing a bit storage device defining a first state for generating a mismatch signal.