The numerals are (in)correct. (Fan Creations)

by Beorn , <End of Failed Timeline>, Sunday, May 04, 2014, 13:34 (3859 days ago) @ DaDerga

The wallpapers are fantastic. Lovely job. There'll be no need to alter the Titan one I'd imagine.
http://gwydir.demon.co.uk/jo/numbers/roman/
"The Romans themselves were not so fussy. There is a Roman tombstone in York, England, of Lucius Duccius Rufinius, who was the standard bearer of the VIIII legion (9th), and was XXIIX years old (or 28)."
–From the linked article.

Heh, I'll say that a tombstone is an unfortunate place to make such an error. But just because someone did it wrong on a relatively permanent surface doesn't mean that the error is in fact "correct". A typo is still a typo. I don't know what the Roman education system looked like, but I imagine there were many in the Roman armies who did not know how to read or write.

Who knows, maybe the letters on the Titan banner aren't even Roman numerals! Maybe they're someone's initials… With lots of X's and I's… :-\

Edit: Okay, I checked the Wikipedia page on Roman Numerals, and they have a whole section on Alternative Forms that says the numeral system was rather fluid back in the day, so your example is not wrong. I would expect, though, that a Roman Numeral system in Destiny would reflect the more recent and codified version that we use today, but maybe the non-standard form was very intentional on Bungie's part. Maybe it's intended to help show how much of human history was lost with the fall of the Golden Age.