|MadSci Network: Physics|
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.
Try the links in the MadSci Library for more information on Physics.