Technical question and answer (Q&A) sites such as Stack Overflow (SO) have become increasingly important for software developers to share knowledge and contribute to communities. Despite their success and prevalence, navigating the knowledge on these sites remains challenging. To make the posts vivid to users, the Stack Overflow platform allows users to write and edit posts with Markdown or HTML, so that users can leverage various formatting styles (e.g., bold, italic, and code) to highlight the important information.In this study, we carry out the first large-scale exploratory study on the information highlighting in SO answers. We observe that overall, information highlighting is prevalent on SO, i.e., 47.6% of the answers have information highlighted. More specifically, 38.5%, 11.3%, 7.2% of the answers use Code, Bold, and Italic, respectively. Besides source code related content (e.g., identifiers, and programming keywords), users also frequently highlight updates (e.g., updates of answers), caveats (i.e., a reminder or warn of in which context or condition the provided solution works or does not work), and reference. Our findings provide insights for future research, e.g., future research should consider the highlighted content for the downstream tasks that leverage information from the SO answers.