http://mycoins.co/german-5-mark-zeppelin-commemorative-coin-1930-a If yours is real, it looks like an exceptional proof. It must be an a modern reproduction no?
Some restrikes of this 5 RM. got a "999" mark or a year of the restrike. I can't see anything on these photos that would say its a restrike and not an original. To be sure, make sure its silver and also the weight is correct, 25g. This would be a very expensive coin, it would make sense slabbing it.
here're more pictures of the coin http://sky.geocities.jp/drivearea/009.JPG as per seller the weight is 25gr, diameter approximately 35mm some people raised my doubts regarding the coin with it being restrike ... though no real reasons were provided
As Taxidermist mentioned, there are "restrikes" (not official but third party) of that piece, but those would have to be recognizable - different metal, added year, etc. See here for example. Does not seem to apply here, so this is either genuine or counterfeited. I would not buy a coin like that, say, via eBay. But if it's from a dealer with a good reputation who guarantees the authenticity of what he sells, why not? Christian