Printer identification based on a printed document can provide forensic information to protect copyright and verify authenticity. In addition to intrinsic features (intrinsic signatures) of the printer, modulating the printing process to embed specific signature (extrinsic signatures) will further extend the encoding capacity. Some features generated by modulating EP process such like raggedness of the edge in the text, can be designed and utilized to help develop the extrinsic signature. By increasing the level of modulation, which increase reliability of detection and thus capacity, we can drive the extrinsic signature to a point without perceptual degradation of the image quality. In this paper, we will investigate embedding extrinsic signature in text documents using laser intensity as a signal modulation source and develop extrinsic signatures using both frequency as well as amplitude modulation. Preliminary experimental results showed that it is feasible to embed detectable extrinsic signatures in text characters without degrading perceptual text quality.