Who are what now?

Many years ago, in a seemingly more innocent and happy age, back in about 2000 or so, I worked in a building with an elevator in it. I still work in a building with an elevator in it, in fact three elevators, but it's a different building now and this really isn't the story I'm trying to relate now, so let's try not to get sidetracked.

The building I was in had an elevator, I think I mentioned that. One day I took the elevator to the balcony level to partake of a cigarette and noticed something strange scrawled on the inside of the elevator doors.

The inside of the elevators were painted black making a rather effective chalkboard, of which someone had taken the advantage to use as same. Scrawled in white chalk on the inside of the elevator doors in a rather workmanlike script;

"Tuners are cats."

I pointed this out to my workmate Glen, who was as equalled puzzled as I as to the meaning of the phrase. There was insufficient space between the doors for a hand to reach in and scrawl a coherent sentence. It must have been done before the doors were installed, or perhaps during maintenance. But what did it mean?

I have a couple of theories as to the significance of this communication, but today I invoke the great hive mind of teh intartubes - what does 'Tuners are cats' mean?