IIRC first serving you got cafeteria style. But yes, when you wanted seconds, thirds, etc. you raised the flag for a server. The flag part made it easy to track down. It was called Pancho's, and apparently the one in MSY had a local following.

New Orleans restaurant critic Richard Collin described the restaurant as “a miracle,” and he listed its sopapilla as a “platonic dish,” signaling that he held it in the highest regard.

“Pancho’s food is excellent regardless of price,” he wrote in 1973, when the buffet cost $1.49. “At the price it is unbelievable.”

Things evidently started slipping fast, however, and by 1976 the same critic wrote that “(t)he food is now gross, and large quantities simply underline the lack of delicacy.”

Pancho’s later moved to Veterans Memorial Boulevard in Metairie, and despite Collin’s assessment it went on to win many new fans over the years until it was shuttered by Katrina in 2005. Prior to its reopening in 2009, thousands of people joined a Facebook group to share memories of their meals there and support the restaurant’s rumored return.