E-Petitions have become an important aspect of political participation via the Internet, allowing citizens to publicly support political issues. This paper reports findings from a study on the E-Petition Platform of the German Bundestag, combining an analysis of the platform's database (period: October 2008 to January 2013; n = 2,653 petitions) and an online survey among the platform users (Fieldtime: August/September 2013, n = 244 participants). It reports findings on signature patterns over time as well as between different topical areas, among them evidence for a very uneven distribution of signatures across petitions, for a “spill-over effect” where popular petitions draw attention to the platform to the benefit of other petitions, and for a higher activity of male users. The study also investigated the effect of the introduction of the pseudonymous co-signing option in 2012: No significant change in the amount of signatures was observed, but the majority of co-signers are having a pseudonym rather than their real name displayed in the public list of signatures. This seems to be mainly a “default effect”, but results from the survey also show that users consider pseudonymous signatures as serious as real-name support.