Mail Rule to detect a character string

I am attempting to find a method to create a mail flow rule to detect the character string PIN.

I want to encrypt any message where a user may inadvertently send their PIN number for their Credit card or Debit card.

When I create a rule to detect when "any of these words" I insert PIN as a word.

This works, but it also detects other word with PIN such as "mapping" or "hoping".

I also tried \sPIN\s this had the same results.

Is there a method that can do this?