This is a fake that is quite commonly offered on the internet. This particular design has been around since the '70's. Frederick J. Stephens writes about these in his book 'Reproduction? recognition!: frauds and reproductions of German Third Reich blades', calling them 'fantasy knifes', as they have no historical derivative.

Here's a picture of a older reproduction of this knife. You will see it shares the very same serial number.

The fabricators of this item were most likely inspired by objects like this. Take note of the details. Also take note of the price. You might notice some areas on this piece are blued out, that is to stop fraudsters of making correct reproductions of these kinds of objects.

With nazi-era collectibles a good rule of thumb is to assume it's a fake unless it is very expensive and sold by a very reputable salesman. Of course that is the very same reason they tend to be made quite frequently as people get lured in by being able to buy something seemingly very valuable for a very low price.

A quick google of the serial number or 'ss streifendienst knife' turns up multiple forum posts of people asking for information about a copy of this weapon on various forums. I suggest always researching the object before you aquire it.