Hi there,
That does look like an epitaxial planar switching diode.
http://p.globalsources.com/IMAGES/PDT/B100129...-Silicon-Epitaxial-Planar-Switching-Diode.jpgbut diodes usually have a mark for the cathode that
can't be easily erased.
Are you positive it is a diode? If it has no response with
the diode test of the multimeter, i think it can either be a broken diode
or a busted 0 ohm resistor [never seen one with that transparent insulation].
Anyway, pictures of the board may help too.
Based on the questions I've read here in the forums, my best guess is
that diode most likely came from a boost regulator circuit / an AM demodulator circuit / or a full/half wave rectifier circuit.
Regards,
Justin