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.