Require users to include topics in stream messages
Note: This feature can only be controlled by organization administrators.
By default, users are not required to specify the topics of messages to streams; if a user sends a message without a topic, the message's topic is displayed as (no topic). Any other user can then edit the topic of such a message to set a topic.
Some organizations prefer to require that every message to a stream includes a topic. Organization administrators can choose to enforce the use of topics in new messages to streams:
Select the Require topics in messages to streams checkbox under the Message feed section.
Click on the Save changes button to save any changes you made to your organization settings.
Once this setting is enabled, any users that attempt to send a stream message without a specified topic will see a warning in the compose box and will be prevented from sending their message until they specify a topic.