The comments box comes with a number of formatting options, including emojis. Redbooth uses Markdown as the language to write comments. Click on the A button to the right of your comment box to view the options available.
You can discover more emojis to use here.
Task comment history
There are two different options when it comes to seeing trail messages and comment history in all tasks. The comments option shows just that (comments!) and the all activity option will also display any edits to assignees and due dates.