Re: Electromagnetic radiation from antimatter

To an outside observer, the radiation would appear identical. 

The situation would be slightly different, as the positrons would be
flowing in a direction opposite to the direction of the electrons in a
normal wire, with respect to the phase of the outgoing radiation...but
that's just an issue of timing.  Whatever was driving the wire wouldn't
know the difference.  The current in the wire would be the same with
respect to the radiation (because current doesn't tell you whether the wire
is matter or anti-matter), and the radiation wouldn't differ in any way.