When replying to a post on the noticeboard, you can either write a comment or you can add a reaction.
To add a reaction to a noticeboard post, click on the Add a reaction button.
This brings up the emoji picker, where you can browse through and find the emoji that best fits your reaction, or use the search bar to find something specific.
You can see who has reacted to a message by hovering over the reactions under the post.
To remove reactions, simply click on the reaction you want to delete underneath the post.