I've noticed that a lot of email spam puts "codes" into the subject line, probably to track their success rates. The code is some random-seeming string at the far left of the subject line, usually like this:
Subject: Save on FREE Penis Enlarging Ink Jet Cartridges!!! AS93KR88Today I received this spam - note that the code goes with the rest of the subject nicely:
To: some address
From: "Barbara Love" <45tyger@msn.com>
Subject: How to double your money! POT