Back when Southwest first started in 1971, they had a "love" theme. Their peanuts were called "Love Bites". Their cocktails were called "Love Potions". Their automated ticketing kiosks were called "Quickie Machines". Their first print ad featured their total schedule and the slogan was "How do we love you? Let us count the ways."
In 1974, after the other airlines had moved to DFW and Southwest remained at Love Field, their slogan was "Love is still our field".
In 1978, after Southwest had inaugurated service to several more cities, their slogan was "Were Spreading Love All Over Texas."
These print ads, as well as many others, can be seen on Southwest's website at
Also, be sure and click on the link for the video ads and one of them is the TV Commercial featuring the "We're Spreading Love All Over Texas" song where the passengers sing and dance their way onto the plane.
You mentioned Texas International's "Fly for chicken feed" billboard. But did you know that later, Texas International also switched to a "Peanut" theme. Their Fares were called "Peanut Fares". On one of their timetables during the 1980's, they had peanuts with with wings and a tail that looked like a plane.
On another one, they had a "peanut pilot". It was a peanut wearing sunglasses and a pilot's cap. You can see what I'm talking about on this site which features images of those timetables.
I think it might have been TI's, but it didn't last very long, because looking at those timetables, the Peanut theme started in the spring of 1977.
Texas International had another slogan "We know the Territory".
Also, National's "I'm (Girl's Name). Fly Me." And "Watch Us Shine" was clever since their logo was the sun king. Also, "You're a National Priority."
Disclaimer: I'm not old enought to actually remember that slogan, but I've read about it.