Like most consumers, I associate the phrase “thank you” with Citigroup THANKYOU Marks, which the financial-services giant uses in its customer rewards programs. When I hold the door open for a little girl and she says “thank you,” I suffer a moment of confusion. How has this child become employed by Citigroup, and why has my act of courtesy earned me THANKYOU Mark rewards? But then I remember that, oh yeah, trademark violations have diluted the THANKYOU Mark brand to the point where people started using it in non-rewards point contexts. It’s the kind of infringement on intellectual property that has become too common in the modern world. Fortunately, Citigroup has fought back against such lawlessness by filing suit against AT&T for using “thanks” and “AT&T thanks” in its own marketing materials.