In the end of Total Recall (2012), what does this number stand for?

That's not a 21, that's another language. It's a Korean transliteration of the name 'Rekall' so people who read Hangul (the written Korean language) and not English can understand the ad. Fortunately, Hangul is relatively easy to read, and is well-documented online. After some googling, I found a few tutorials, and a handy Wikipedia reference. Hangul has each 'letter' be a syllable, which combine more fundamental vowel and consonant symbols. Here that means we have 2 syllables - "Re" and "kall":

• "Re" would be turned into a syllable combining the "r/l" symbol "ㄹ" with the "i" or "ee" symbol "ㅣ"


• "kall" is a bit more complex. This uses 3 symbols, which I had to do more googling to get an explanation for. The syllable starts with the "k" symbol "ᄏ" with the vowel "oh" symbol "ᅩ". The tricky part is that the syllable ends with an "r/l" symbol "ᆯ", which is denoted by being on the bottom of the combined syllable symbol.

Therefore it's "re"->리 + "kall"->콜 = 리콜