Since digital video data can be easily manipulated, the importance of video authentication is increasing. We propose a watermarking technique that is simple to implement, yet quite effective for H.264/AVC. The proposed watermarking scheme inserts a watermark bit on the motion vectors for inter-coded macroblocks or on the mode number for intra-coded macroblocks. A scheme to watermark skipped macroblocks, which are vulnerable to forgery, is also proposed. The new watermarking scheme shows high watermark payload with small image quality and compression power degradation. The run-time increase for software implementation and design overhead for hardware implementation, of the proposed watermark, are very low due to the simplicity of the algorithm.