In this paper, we argue that social activity indicators for reading activities in Usenet newsgroups are valuable for social navigation in newsgoups. Reading messages is a frequent as well as an important social activity when interacting with Usenet newsgroups. Specific indicators are required as newsgroups do not reflect reading activities. Appropriate indicators for these hidden activities, however, would provide valuable insights in the social dynamics in particular newsgroups as well as in the interests of individual newsgroup users. In what follows, we present a framework that visualizes Usenet reading activities for social navigation purposes. Social navigation is an active research area that aims at exploiting the behavior of crowds for supporting users in navigating information spaces. We present an implementation of social activity indicators for reading activities in newsgroups, discuss user experiences, and outline future research directions in this area.