In TrueType/OpenType, the first glyph in the font is used as the "missing glyph".
And for Postscript fonts systems often take the bullet character in the font as the "missing glyph" symbol.
However printers are very erratic in what they do.
Whether a character like ASCII 0x01 (probably in a data file in error or by mistransliteration) will be rendered by a printer as a missing glyph symbol or space seems to depend on which printer driver is used and often on settings within that driver.
Jim Allan
