It seems to be a thing in various continental European regions. I'm most familiar with seeing it done in French. From Wikipedia:
>Capital or small capital Roman numerals are widely used in Romance languages to denote centuries, e.g. the French xviiie siècle[26] and the Spanish siglo XVIII mean "18th century". Slavic languages in and adjacent to Russia similarly favour Roman numerals (XVIII век). On the other hand, in Slavic languages in Central Europe, like most Germanic languages, one writes "18." (with a period) before the local word for "century".
And the famous Mexican beer Dos Equis gets its name because it was created in 1897 and was celebrating the soon to be 20th century (XX, Dos Equis in Spanish).
>Capital or small capital Roman numerals are widely used in Romance languages to denote centuries, e.g. the French xviiie siècle[26] and the Spanish siglo XVIII mean "18th century". Slavic languages in and adjacent to Russia similarly favour Roman numerals (XVIII век). On the other hand, in Slavic languages in Central Europe, like most Germanic languages, one writes "18." (with a period) before the local word for "century".