Federal tax refund check fraud prevention

Does anyone know what sort of anti-fraud devices are on Federal tax refund checks, e.g. hidden codes that must convert to the check amount? Out of idle curiosity, I've always wondered about it every time I've looked at my refund check. The check amount seemed to be printed using some ancient technology, industrial-scale, mono-spaced font, impact printer and it always looked like a decimal place could be moved and a zero added fairly simply so as to not be immediately noticable by anyone not looking for it. Of course, I never seriously considered doing such a thing, but from the looks of the 1960s era equipment used for printing, certainly others must have and there'd have to have been implemented some sort of anti-fraud countermeasures to guard against it.