Abstract: An apparatus for forming an indicium in a stream of moving signatures, consisting of a signature displaced laterally from the stream and corresponding to a predetermined count of signatures, comprises an idler roller mechanism connected with a rotatable idler roller shaft and a series of vacuum heads located adjacent to and downstream of the idler roller mechanism. The vacuum heads are mounted to a vacuum head shaft laterally movable with respect to the signatures. A detector such as a laser detector coupled with a counter is used to actuate the system. When a predetermined count is reached as determined by the detector and counter, the idler roller shaft is caused to rotate to lower the idler roller and the signature corresponding to the count contacts the tops of each vacuum head. Simultaneously, a partial vacuum is formed in the recessed vacuum chamber of each head binding the targeted signature to the heads.