This study explores the role of social media in social change by analyzing Twitter data collected during the 2011 Egypt Revolution. Particular attention is paid to the notion of collective sense making, which is considered a critical aspect for the emergence of collective action for social change. We suggest that collective sense making through social media can be conceptualized as human-machine collaborative information processing that involves an interplay of signs, Twitter grammar, humans, and social technologies. We focus on the occurrences of hashtags among a high volume of tweets to study the collective sense-making phenomena of milling and keynoting. A quantitative Markov switching analysis is performed to understand how the hashtag frequencies vary over time, suggesting structural changes that depict the two phenomena. We further explore different hashtags through a qualitative content analysis and find that, although many hashtags were used as symbolic anchors to funnel online users' attention to the Egypt Revolution, other hashtags were used as part of tweet sentences to share changing situational information. We suggest that hashtags functioned as a means to collect information and maintain situational awareness during the unstable political situation of the Egypt Revolution.