As previous respondents have observed the inscription is not Amharic script and appears to be a repetition of the Roman numerals for 12. The original owner had the artisan go to considerable effort to inscribe the XII motif. It apparently reflected considerable meaning to him.
As Ethiopia is a Christian nation with Jewish elements, I suggest that this is Hebrew and/or Christian numerology. The attached link discusses the significance of the number 12. Other searches will reveal Ethiopian numerology context.
http://www.biblestudy.org/bibleref/m...-bible/12.html
Best,
Ed