Haha, my father and I did that for Battle of Britain and... Mines of Titan, I think, was the other one.

Old anti piracy measure.

Games were on floppies and could be copied trivially. Games also came with a printed instruction manual. If you bought it, you'd have the manual. If you're just playing a copy you wouldn't. So type one word from a specific page so we know you own the game.

wheel that came with monkey island

http://www.oldgames.sk/codewheel/secret-of-monkey-island-dial-a-pirate

It was anti-piracy; you had to have the physical manual to know the correct word.