MDCCCCXX or perhaps MCMXX. I think the first is more authentically Roman, but the second may be more commonly used today, and is shorter.
IV-XVIII-MDCCCCXX You can't repeat a letter more than 3 times in a row with roman numerals, 1500 would be MD 1600 would be MDC 1700 would be MDCC 1800 would be MDCCC With 1900 you can't repeat the C 4 times, you have to minus a hundred (C) from the next thousand (M) by putting a C before the M. So 1900 is MCM and 1920 would be MCMXX (note: the D is 500). Also using Roman numerals, the date would probably be in European format, Ex. day, month, year, So the date would probably be XVIII IV MCMXX.