Seeing a number of boosts for the mug with "I ▯ UNICODE" on it. Funny thing is missing glyphs like that have nothing to do with Unicode.
@wezm @mauve could also be an encoding error, which was (ironically) common before Unicode encoding standards (utf8, utf16 etc).
This is a great blog post on the subject: https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/
@mauve Yes lack of a font with the glyph for the character in question. In that case the text rendering pipeline will fall back on the `.notdef` glyph of the current font. Every font is required to have it as their first glyph. It can look however the designer wants but boxes and things like that are common.