I have no idea what the W means. But from the katakana at the top, it seems to indicate "double seal(sticker) postcard".
All of the cards are presented below. The fronts frequently have multiple stickers. The last scan at the bottom is the back of a postcard. And the scan at the top of this post is the "header" card found in all packs. I don't have scans of the postcards themselves, hidden under the stickers. But you can see the images above which make up the 25 different postcard fronts.