When using unicode characters, regardless of font, it renders as a square and not the desired character. See attached image (red circle). It does however render in the document title and layer list (see green circles on image).
Photoshop does render Unicode characters. In the case where a given character is not found in a particular font, then Photoshop (correctly) displays a missing glyph character, the square you are seeing. The font used for the application, in this case, does contain the indicated glyph, which is why the heart appears there.