If they are highly educated, why not just say "if you use $&, the program slows down heavily", and let the highly educated engineers decide whether it matters or not.

Exactly how is that different from what the original poster wanted?

Anyone know how I can detect the use of $', $& or $' ? Using these variables kills the performance of our application and I want to generate a warning

Better yet, it will help out future users, even though they didn't get your original memo ;-)