Banding is one of the image artifacts for electrophotographic (EP) printers. Due to its origin within the EP process, it can also be viewed as an intrinsic signature of the specific printer. Modulating the EP process to generate banding signals that are below the human visual threshold but can be detected by effective detection approach can further extend the signature capacity. This deliberate banding signal can be viewed as extrinsic signature of a printer. Since modulating the printing process provides significant barrier of entry, it is effective in limiting the attack possibilities and can be an effective method to embed needed information regarding the document and the device it was printed on to provide unprecedented forensic information. One of the key issues with embedding extrinsic signature is the information should not be detectable by the human observer. However, the signature needs to be detectable by a suitable detection algorithm. In this paper, we will propose one method to modulate the exposure of the EP process to embed controlled quasi-periodic signature into a document. Based on the system level modeling and experimental verification of the EP process, machine detectable signatures that are below the human visual threshold can be embedded into a printed document without any perceivable degradation in image quality. Preliminary experiment results confirm our hypothesis that with properly designed control techniques, effective extrinsic signatures can be embedded into a document.