Blind watermarking method is proposed to evaluate data embedding techniques for H.264 video signals with robustness against various signal processing functions. H.264 is a new advanced standard. The applications of video on Internet or wireless networks become very popular nowadays. However, these digital contents can be easily modified and copied by end users. Hence copyright protection, copy protection and integrity verification have become important issues in recent years. In the proposed system, block polarity and index modulation are used to achieve blind watermark detection. The block polarity is determined based on the nonzero quantized DC coefficient in each 4×4 integer DCT block. The block index is the pseudo-quantized block activity that is represented by the sum of magnitude of quantized AC coefficients. The block index modulation is performed based on the watermark and the blocks polarity. The watermark embedding is performed by the index modulation, which modifies the quantized AC coefficient values by a small amount to force the activity to be quantized into a specific region. Simulation results show that the proposed method performs well, and extracts embedding watermark without the original video signal. Additionally, the algorithm is not very complex and appropriate for real-time applications.