Back in the 1990’s, I experimented with putting yellow post-it notes on the outer envelope of my clients’ direct marketing campaigns. In those tests, we saw a 12% to 30% increase in response.
The post-it note was effective for both consumer and business-to-business mailings. However, this direct marketing technique was most effective with business to business.
Since that time, I’ve continued to find it to be effective.
Here is an example:
 

If you have any experience using post-it notes in your campaign, let me know about it! Contact me at [email protected] or call me at (310) 212-5727 for more information.