Honeywell RTH7600D thermostat has the word “Change” on upper left

She should know by now you'll never change . . . John T.

Reminds me of when Gloria explained to her father that his wife Edith was going through the change of life and that's why she was unusually emotional, etc.

And Archie said, "Okay [implying he understood], I'll give you 10 minutes, now change.

On the manual I downloaded from the web, the illustration on page shows "Change Filter" above the room temperature number, and the page is entitled, "Furnace Filter Reminder". The text is, "If activated during installation, the furnace filter reminder alerts you when it is time to replace your filter. Press RESET after changing the filter, to restart the timer."

If OP didn't have the manual, it's freely available on the web. It took me less that 10 seconds to find a pdf of the manual for that model.

My goodness, you're old. I suppose you know who Festus was. Remember Archie Bunker's Place? Carroll O'Conner played Sparta, Mississippi police chief Bill Gillespie on the show In the Heat of the Night. Harold Rollins (unwhite) was Detective Virgil Tibbs on the show. It's on one of the over the air networks now and then and well worth watching.   

Festus has a statue in downtown Clovis, Ca.

Maybe Dennis Weaver who played Chester.

Did you soil your underwear? If so, change it. Good to change it once a month anyway.

City boy.

You worked it backward. Or stopped researching too soon.

On Ken Curtis' Wikipedia page:

"A statue of Ken Curtis as Festus can be found at 430 Pollasky Avenue in Clovis, California, in Fresno County in front of the Educational Employees Credit Union. In his later years, Curtis resided in Clovis."

Well it's nice that they remember him.