Someone on comp.sys.mac.games offered a different explanation for this infamous level name... although it's not clear from the post whether he heard it from Jason, or thought it up himself and offered it to Jason:
>>In the online chat with Jason Jones on EWorld, he said this:
>
>> BungieCorp : ok, you talked me into it. on the last level (which should
>> be spelled "Ignie Ferroque") there are three secret doors
>
>>So it would appear that the spelling in the game is just a typo. (U is
>>right next to I on the keyboard...)
Well, I'm afraid you're all wrong including Jason. I let him know at
MacWorld that the latin was not correct, but he didn't have anywhere to
write it down. The correct latin as intended is:
Inguine Ferroque
The translation is, "By balls and by Iron", or perhaps more colloquially,
"with balls of steel", the implication being that such would be required
to complete the level. The error is not very severe, and it was fairly
easy to figure out what was meant. The first word is simply not declined
correctly, but there is no other possible translation. Any good Roman
would have understood.