This scene is amazing once you realize that Hawkeye didn’t come up with that code. The first-letter-of-names coding system is something Mustang specifically came up with for his alchemy notes. Which means he had confided with her the secret to reading his research. Not even Al knows how to read his brother’s notes, because they’re disguised as travelogues. If you remember the struggle the Elric brothers went through to decode Dr. Marcoh’s research, then you should know how difficult and important an alchemist’s secret code is. But with Hawkeye, she knows AND uses Mustang’s coding system with no trouble at all.