This work presents an analysis of punctuation use in computer-mediated communication (CMC); in particular, the present study aims to describe the pragmatic functions of nonstandard punctuation on Twitter, providing a corpus-driven overview of the distribution and frequency of nonstandard punctuation use, and an analysis of sampled tweets at the individual tweet level to estimate noise levels in the overall corpus. A survey was also conducted which aimed to identify user understanding of the affective content of nonstandard punctuation strings and to identify any possible effects of character repetition. Survey results indicate that linguistic content was the strongest indicator of affective understanding, type of punctuation (i.e., ?, !, and combinations thereof) was a weaker indicator of some affective content, and repetition was not found to be significant. The study argues that certain string types, possibly defined by punctuation type and not count, have large indexical fields of pragmatic meaning available to them, which are bounded by context. In light of these observations, the study also proposes distinctions/categories of punctuation strings and their associated pragmatic meanings