This poster was hanging on my wall for a few weeks before someone got the joke*. Those are (in my opinion) the best kind of posters.
 

To download a high-resolution copy of this image to print and hang in your own classroom, click here:

High Resolution Multiplicative Property Poster.

* For those who need some explanation, the multiplicative property of inequality says that you can multiply both sides by the same positive value, and you'll get another true inequality. In other words, multiplying both sides by 3 (the obvious choice) results in "I <3 U" ("I love you," using texting and internet shorthand).