In this paper, we introduce a new robust watermarking technique, which is called two-level quantization based spread-spectrum (TQSS). In this method, the selected transform coefficients of the cover signal are two-level quantized to a predefined threshold, which is determined by the estimated bound of distortion. The two-level quantizer is again used for watermark retrieval. Thus, the watermark signal is essentially embedded into the polarities of the transform coefficients. Our simulation results showed that TQSS outperformed some common spread-spectrum (SS) methods under a variety of attacks, such as lossy compression, additive Gaussian white noise, filtering, scaling and print-and-scan process.