How to escape mail tags?

How can I escape a tag named [issue] to display it in the subject line like this:
(Assume [issue] is “Recipe Request”)
Subject: [Recipe Request]

These didn’t work:
[[issue]]
\[[issue]\]
[[issue]]

• This topic was modified 3 years, 4 months ago by bobobongo.
• This topic was modified 3 years, 4 months ago by bobobongo.
• This topic was modified 3 years, 4 months ago by bobobongo.
• This topic was modified 3 years, 4 months ago by bobobongo.
• This topic was modified 3 years, 4 months ago by bobobongo.
• This topic was modified 3 years, 4 months ago by bobobongo.