Hint: It's Not the Shiny One

It's irritating enough when people confuse English horns with French horns. (They resemble one another neither visually nor audially.) But then some feel the need to ask, "What's the difference?" For the appeasement of these morons
To tell apart the French horn and the English horn, perform this simple test: Observe whether the object you're seeing is made of metal. If it's shiny, it's not an English horn.
Sticklers will note that English horns do, in fact, have lots of buttons (called keys) that are in fact shiny. However, as the experienced woodwind-spotter will understand, in this case it is the keys that are shiny in their own right and not the instrument.
Let's try a simpler mnemonic. If you see it and think "horn," then it's probably a French horn. If you see it and think, "What's that weird thing that looks like a pregnant oboe," then it's probably an English horn.