Quantized projection technology (QP) is the version of quantization index modulation (QIM) working in the projection domain. It essentially belongs to a double-sided additive embedder. In this article, the concept of sign quantized projection (SQP) is proposed, which differs from the conventional QP when working as a single-sided embedder. Theoretical analysis reveals that SQP has the same probability of miss and probability of false alarm as QP. Also, the document-to-watermark ratio (DWR) of SQP is less than its counterpart of QP by 101g(1+γ) dB.