I don't know if the #57 in the mirror #5775 would represent day #57, which is 2/26 on our modern day calendar that begins on 1/01 every year in the year 2015, but it is one possibility.
However, the actual 57th day in the Jewish yr. of 5775, is the 27th day of Kislev which is the 3rd day of Hannukah, and on our modern calendar would be 12/19/2014.
So these are just 2 possibilities of what the #57 might represent in the mirror # of 5775, or it might represent something entirely different.
However, Hebrew word #57 in Strong's Exhaustive Concordance is "abel"which means "lamenting: mourn (-er, ing)."
Greek word #57 in Strong's Exhaustive Concordance is "agnostos" which means "unknown."
If you were to fold the Jewish year of 5775 exactly half that begins on Rosh Hashanah, Tishri 1, 9/25/2014 through Elul 29, 9/29/2015, which is 370 days, it would be folded in half with 185 days in each half. The center point would fall at midnight between 3/28 & 3/29/2015 which are Nisan 8 & Nisan 9 in the Jewish yr. of 5775, but to complicate things even further and get more technical about the Jewish year of 5775 actually begins at sunset on 9/24/2014 and ends at sunset on 9/28/2015. So it looks like exact middle of the Jewish year of 5775 would be at sunset on March 28, 2015 if I figured this out correctly. (It's also interesting to note that the 185th day in a non-leap year on our modern calendar is July 4th which is the U.S. Independence Day that began in 1776. It makes me wonder if the U.S. will be judged and/or destroyed on that day.)
One last thought is if you were to cut our modern day calendar of 365 days in half with 182.5 days in each half, the exact center would fall at 12 Noon on July 2 in any non-leap year, or at the end of July 1st at Midnight in a leap year, and of course, July 2 is two days before the U.S. 7/04 Independence Day that began in 1776, and the U.S. would be 239 yrs. old on that day in 2015.