I think they're books for party membership/ paying party dues.
Exactly, thanks mate. I googled it after your first comment and found them straight away. Kinda cool little things, I wonder what the paragraph says about the guy in the big book.
No problemo, sir! I have a smaller book in my collection.
The larger books were kept as a sort of personnel file at the local Party HQ where the person was registered as living (almost like a wehrpass whereas the smaller one is akin to a soldbuch). Most people when the wall fell went to these HQ's and removed their books and destroyed them, some people, however, sold theirs. The smaller book is a "Party ticket" which IDs you as a member of the Party and as you surmised is a record of your dues payments. Hope this helps...