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Dejan Zivkovic of Sacramento flies a lot. He’s always wondered something about the three letters on his boarding pass.

“I would always see SMF and always have the question in the back of my mind of, what does SMF actually stand for?” he said.

The airport isn’t shy about their letters. The terminals sport signs with slogans such as, “easy as SMF”. They even built a social media campaign around it in 2014, asking "What does SMF mean to you?"

But many don't know the history of the letter code. According to the airport, the letters actually stand for Sacramento Metropolitan Field. It’s a reference to an old airport that was on Freeport Boulevard. When it moved in 1967 its current location and became Sacramento International the code letters came with it.

Zivkovic said he understands why they would have kept the letters during the move.

"I think it totally makes sense now," he said. "I think it was easier to stick with the airport code they already have and it would have been easier on them with FAA regulations and whatnot to keep the paperwork low."

Odd airport letters are pretty common. Airfare Watchdog keeps a list of 15 strange letter codes,  and Sacramento isn’t even on it. Fresno’s airport is though: its letters are FAT — Fresno Air Terminal.