I've actually had a similar struggle with the incessant but spammy recruitment emails, that I was able to fix almost perfectly. In the "Summary" section of my LinkedIn[1], I have a sentence that says this:
"If you wish to contact me, please put the word 'Waffles'
in your message. It sounds silly, but it lets me know that
you have taken a little time to asses my profile, rather than
mass messaging people based on a keyword search."
"Waffles" will never be added by coincidence, so if I ever see that in the subject line of an email, I know that the recruiter has actually read my profile, and took the time to write a custom email to me. If it doesn't have the word "Waffles", I just ignore/delete it. It has dramatically improved the quality of emails I get from this vector
I see you worked for Jardine. I own a company that is also a SEMA member, and for those programmers out there looking for work, most of the members of SEMA could use advanced technical help. SEMA.org is the automotive aftermarket industry group and is for the most part not very technical. In other words they need a lot of help. They just launched a big initiative this year that has the bold goal of standardizing industry data, so they are just now getting into the computer age with gusto (to be fair, many larger companies have been using EDI for years).
Sorry for wandering off topic. I have used a method similar to your "waffles" technique when hiring for positions. It reduces the 100's of applicants for a job down to a few, simply because most people won't read your postings clearly. It has saved me hundreds of hours in the recruitment process.
[1] http://www.linkedin.com/pub/joe-cortopassi/24/76b/5b9/