Definition of SQUARE ML (㎖) This is a very simple thing, I suppose, I'm having hard time to find out, what is the meaning of Square ML (㎖) symbol? Square MiLe, Square MilliLiter, Square Maximum Likelihood, or totally something else?
I can find these symbols belonging to the physical symbol set in unicode set starting from:
0x3371  13169   SQUARE HPA  ㍱

and going to:
0x33DD  13277   SQUARE WB   ㏝

http://www.ssec.wisc.edu/~tomw/java/unicode.html
Along ML are: 
0x3395  13205   SQUARE MU L ㎕
0x3396  13206   SQUARE ML   ㎖
0x3397  13207   SQUARE DL   ㎗
0x3398  13208   SQUARE KL   ㎘

And yes, this seems to be more of physics topic, not that much mathematics...
 A: Disclaimer: This post will use a lot of unicode characters that may not display properly in some environments.

The characters in the CJK Compatability block are mostly symbols for units used in Japanese, with some crossover into other languages like Chinese and Korean. Most of them have a name in unicode with "SQUARE" (as in SQUARE ML) because the character is made from multiple symbols designed to fit the square space that a character would fit in for proper Chinese/Japanese/Korean typesetting. For example, compare the spacing of "c""m" vs. "cm" in this string:
 三ｃｍ三cm因.
㎖ means milliliter, and this meaning is shown on the Japanese and Korean wikipedia pages for "liter". You can also see is referenced in math courses. For example, a middle school math student is asking about the relationship between ㎤ (a single character for $\mathrm{cm}^3$) and ㎖ here. 
There are many other units and related symbols in the CJK Compatability block, including ㏑ for $\ln$, ㏒ for $\log$, ㎯ ($\mathrm{rad}/\mathrm{s}^2$) for the SI measure of angular acceleration, ㌫ for "percent", and ㌦ for "dollar(s)", etc. The last two are written in Japanese phonetic characters.
