Although social network advertising has become part of the online marketing strategy, there is still a lack of research related to the interaction between brand awareness and advertising contents in social network advertising. Using the semiotic theory to explain the interaction in social network advertising, this study introduced sign-interpretation-object triangle to analyze the interactions of advertising content and brand awareness as signs, users’ experience as interpretation, and social networks advertising effectiveness as object moderated by social facilitation. This study was made in an experiment followed by an online survey, which contains 303 participants in Mainland China. This study shows some major findings. There is an interaction effect on advertising content and low brand awareness in a social network. The moderating role of social facilitation is significant in advertising content with high brand awareness.