Numa

"A is the first letter, so A is one," Numa said. "B is two, C is three, all the way to Z, which is twenty-six. So I just replace each letter with its number. The word CAT — C is three, A is one, T is... A-B-C up to T, that's twenty — becomes three, one, twenty. I write it with little dashes so the numbers don't run together: 3-1-20. To anyone glancing, it's just digits. But a solver who knows the trick counts each number back into a letter and the word steps out." Numa tapped the card. "Letters into numbers to hide, numbers into letters to find."

"Here's the thing I always tell people," Numa said, "so they don't get stuck: you have to separate the numbers clearly, or twelve could mean the letter L, or it could mean one-then-two, A-B. So I always put a dash or a space between each letter's number. That little bit of care is what keeps my clue fair — a solver should have to know the alphabet's order, not have to guess where one number ends and the next begins. And the alphabet-in-order is the whole key: if you can count A, B, C to twenty-six, you can build my code and you can break it. It hides words in plain-looking digits, but it never locks out anyone who knows their letters."

The member tried it on the word GO. "G is... A one, B two, C three, D four, E five, F six, G seven. And O is... fifteen. So GO becomes seven, fifteen — 7-15." They wrote it with a dash. "And to solve it, count seven letters in for G, fifteen letters in for O — GO." They laughed. "It looks like a bus number, but it's a word." Numa nodded. "And because you dashed them, nobody will read the seven-fifteen as some other letters. Clear numbers, fair puzzle."