Well this one's actually deceptively easy- it looks realisitc, the fonts and layout aren't suspicious, but the faker blew it in the most obvious way right off the bat: the unit type is completely nonsensical; there's no such thing as an Infanterie-Ersatz-Abteilung, SS or otherwise. There was only the Infanterie-Ersatz-Bataillon. Different unit types had different organization types- those that were organized into Abteilungen were Panzer, Nachrichten and Artillerie units, just to name three, while Infanterie-types (Infanterie, Grenadier, Panzergrenadier, Jäger, etc.), Pionier, MG, etc. were in Bataillone; and it was always that one, never the other. So fakers make obvious mistakes like this one by mixing up the types and creating Infanterie-Ersatz-Abteilungen, Nachrichten-Ersatz-Bataillone, and so on. The Waffen-SS used the same rules.
One needn't even memorize these types- there are all kinds of lists like the Ersatztruppen section of the Lexikon der Wehrmacht site, all the useful photos on emarken.de and so on.
There are further problems with this disc too:
1) Even if the faker had put 'Btl.' instead of 'Abt.' and made his error less-easy to spot, it'd still be fairly obvious because there was no 'SS-Infanterie-Ersatz-Bataillon 8'; there were only a handful of 'SS-Infanterie-Ersatz-Bataillone', each a 'named' one like 'SS-Infantiere-Ersatz-Bataillon ,,Westland'' ' and 'SS-Infantiere-Ersatz-Bataillon ,,Germania'' '- none with a number.
2) The 'FRW' mark indicates the disc was supposedly issued to a 'Freiwilliger', a 'volunteer' but not in the sense of a regular citizen volunteering for service. I've never been quite clear just who they'd be or what the difference is between them and the HIWIs (Hilfswilliger- helpers- who were, I believe, POWs), but I have the impression both were associated with field units, not Erstaz ones, and that they had their own roll, they weren't just given regular unit roll discs; so this disc could have it wrong that there even were 'Freiwilliger' associated with this Ersatz unit, and that there'd been nearly 600 of them over time in this one Kompanie!
Ohhhhh- pillage then burn...