In my experience that subject line does nothing. I've put things along the lines of "Urgent" "Time Sensitive" "Failed purchase" "arena lock out" and none of those actually did anything. The only times I ever got a response in a timely manner was when the game first started with a different support team and more recently when I managed to engage with a team member outside of the support ticket.
Besides none of this addresses the fact that tickets get marked resolved but the problem still exists. How many "Arena Refresh stole 10 Ironite" tickets are out there and closed even though they STILL have yet to fix that issue.