> to use the square root character (√) as a checkmark ([filtered out])

IMHO that's an old-school-ism: I've never seen that in the post-Unicode world, but I recall its being common in the days of PC-compatibles, when square root was one of the ~256 characters you got, and checkmark wasn't, so you made do. In the same bucket with "using eszett (ß) as a lowercase beta (β)" or "using upper-half-of-integral (⌠) as a long S (ſ)." In fact Wikipedia's footnotes mention all three of these substitutions. (Or "using hyphen-minus (-) as a minus sign (−)." ;))

[1] - https://en.wikipedia.org/wiki/Code_page_437

[2] - https://knowware.dk/dos56/norton-commander-1.shtml — see the last two screenshots on this page, from Norton Commander