Are perfins still commonly used today on U.S. Postage?
I had thought that was an obsolete method of company identification/security for stamps, until I came across a Marilyn Monroe stamp that was perfined by the local utility company.

I'm not exactly sure why a utility company would use postage versus a meter, but it was an invitation piece to an event (so maybe they just wanted it to look more personalized by using a stamp).
My question simply is: "How common are perfins on modern-day stamps?"