I have always been against in a lot of ways people selling on this kind of item real or fake of the band or any other band for a bit of personal profit. It does not hurt to donate some of the money to a chosen charity.
There has been some great auctions on ebay for Motorhead signed guitars where the money has gone to a worthwhile charity, and the band has signed them and there can be no doubt to its authenticity.
Motorhead have always been great for things like this especially when it benefits less fortunate people.
The Motorhead Collectors Guide has the proper signatures and that should really be the only reference you need to compare if they are real or not.