Several threats, such as misinformation and hoax, exist in social media as a frequently used technology to exchange information. That kind of threat can be prevented if the reader can verify the message’s content integrity and source authenticity. In the previous solution, Ahvanooey et al. proposed an invisible watermarking scheme, ANiTW, as a tool to verify social media message integrity and source identification. However, ANiTW is still vulnerable to undetected tampering attacks. Moreover, ANiTW has no tools to authenticate the message source. The proposed method aims to improve ANiTW as a social media’s message content integrity verification and message source authentication tools. In the proposed method, part of the message hash and signature generated by the IBS scheme is introduced as a watermark to increase the security aspect of ANiTW. A novel bigram-based character encoding is also proposed to increase embedding capacity and invisibility. Based on the experiment and analysis result, it is proven that the proposed method can perform better than ANiTW in the security, embedding capacity, and invisibility aspects. For the security aspect, based on the experiment result, the proposed method can detect modification in watermarked cover text, whereas ANiTW cannot. In addition, the proposed method can verify the validity of the message’s source (author), preventing a possible impersonation attack in ANiTW. The proposed method can also increase the maximum embedding capacity of ANiTW with a maximum improvement of 260%. Furthermore, the statistical and visual invisibility of the proposed method also performed better than ANiTW