How can I categorise tickets as 'Information Security Incident' Yes or No.

[Candy Tricia Khohliwe]

Once the ticket is categorized it can then be a resolved ticket.

[Jack Brickey · Accepted solution]

If I understand your requirements you should simply create a custom field single select with Yes and No as the options. I assume you will want to require the field to be updated maybe at create or as a transition as well. You may wish to set a default value (No?). 

[Candy Tricia Khohliwe]

How can I go about having the field updated at creation or when transitioning?

[Jack Brickey]

Two methods of using Classic project. 

• Transition - edit workflow and on the specific transition you can add a screen that pops up to display the field. Also add a Validaor on the transition require the field. You could do this using a post function but I assume that you want the user to select the option. 
• at Create - similar to Transition you would add a create screen to the create transition

if you have not edited workflows and done this before I recommend this document- https://support.atlassian.com/jira-software-cloud/docs/what-are-jira-workflows/ 

[Candy Tricia Khohliwe]

Thanks Jack!