By default, Update viewers have the option to add an emoji reaction to your update.
If you'd like to toggle reactions off you can do so by clicking the 3 dots in the top right-hand corner of a draft of an update. From here, toggle reactions to the off position and they will be removed.
If you decide to keep the reactions toggle on, then update viewers will see the below image at the bottom of your update and they can then choose to send the emoji reaction.
Please let us know if you have any additional questions!