So, on Niconico on Jan 8th, there's a special broadcast of Seiko Oomori called:
『Your Number Is 1～1500 ～美マネは書きません～』
Or:
"Your Number is 1 ~ 1500- The Manager Didn't Sign It"
YEP. THATS THE NAME OF THE SHOW.
And it's exactly that. Seiko Oomori signing all the boxsets.
At least we can be 100% assured that we're getting a legit signature.
That's what I call fanservice.
More info here:
http://oomoriseiko.info/news/detail.php?id=1030578