European. That is, there's a decimal comma, and the dot is a thousands separator. Sometimes a space is used for the separator, but is sure to confuse the reader when a printed text breaks a line on it, so dot it is.
Due to the influence of locale blind software, the American format of numbers is used in some places (some older cash registers, perhaps  going through the dozen receipts cluttering my desk, I found none such).
Ordinal numbers are regular Arabic numbers followed with a dot: 9. means ninth. Roman numerals are ordinal by definition. A Roman numeral with a suffix, or an Arabic with an ordinal suffix is written by illiterates. Roman numerals were widely used to denote the month in the old date format.
