SLA use for Subject Line

The best way that I can see is that you have a trigger looking for that specific subject line and then it adds a tag/field. Then within SLAs, you can add that tag/field as an option so that the SLA only applies to the tickets with the specific tag

You can define an SLA based on the subject of a ticket in Zendesk by following these steps:

• In Admin Center, click Objects and rules in the sidebar, then select Business rules > Service level agreements.
• Click Add policy and enter a Policy Name and a Description (optional).
• Select the Conditions for the policy. You can use the Ticket: Subject condition to match tickets based on the subject text. For example, you can enter “urgent” to match tickets with “urgent” in the subject.
• In the Reply targets, Update targets, and Resolution targets sections, enter a time target for each metric and ticket priority. You can choose from different metrics such as First Reply Time, Next Reply Time, Periodic Update Time, Pausable Update Time, Agent Work Time, and Requester Wait Time.
• If you’ve set a schedule, select either calendar hours or business hours for Hours of operation for each priority.
• Click Save. The SLA policy is created and applied to tickets that meet the conditions.

For more information, you can check out these articles:

• Defining SLA policies
• About SLA policies and how they work
• How can I troubleshoot common SLA issues?

Brandon already mentioned the best way to figure out your topic.

Please have in mind that the group SLA's will also offer additional features.

Regards, Stephan

Adding here that you can create a Trigger based on Subject contains the text Shipping Incident.