Here are some fotos I recently took in St. Annen Museum in Lübeck:
Its the Altar of the "Gertrudenbruderschaft der Träger" (Gertrud brotherhood of the porters) from 1509 and it shows St. Anne and the Holy Kinship. Two of St. Annes relatives are carrying a girdle book :-)
Here you can see the two possible methods in "wearing" a girdle book - in your hand or tucked through your belt.
A really nice details is the red colour of the cover the lady is wearing through her belt in comparison to the simple black cover of the other girdle book. Note the folds of the cover under the clasp - the leather extends the cover on all sides, not just on the lower part. This way the book is completely protected all around.
The little circular mounts on the front and back are also a protection besides beeing decorative: When you put the book on a table, only the mounts touch the surface, the leather (or in my case, even more important the silk) doesn't come in contact with it.
I already bought little mounts for the book from Lorifactor. Cute little brass flowers originally intended to be belt fittings, but they look just like the ones used for books :-)