Just going on the vile presentation alone I'd be sceptical.
The image is pretty small. Any date on it?
I hope you don't really mean that you have no idea at all as to what a Bowie sig. should look like. Just type in "Bowie autograph" in your Google bar, hit "images" and voila! There may be some fakes in there but there should be plenty of good ones too.
There was no date on it was offered at an auction. I know Bowie had changed his sigs and not knowing what era it was from I didn't know what to look for. I passed on this one and bought a real one.