Not emojis but glyphs. There is the title, and there is metadata. Round brackets are already potentially in the title, as part of it (this submission is an example). Square brackets are for elisions, to complete the literal title. Other brackets do not seem to be immediately suggesting metadata. The article's datation is metadata. It makes sense, if one used the round brackets, to apply a tag to signify it's metadata, and to use a glyph is more efficient in more sense than writing a string (such as " (age/date/from: ...)" ).
Not emojis but glyphs. There is the title, and there is metadata. Round brackets are already potentially in the title, as part of it (this submission is an example). Square brackets are for elisions, to complete the literal title. Other brackets do not seem to be immediately suggesting metadata. The article's datation is metadata. It makes sense, if one used the round brackets, to apply a tag to signify it's metadata, and to use a glyph is more efficient in more sense than writing a string (such as " (age/date/from: ...)" ).