These cards were part of the sub-genre of cards and cardboard 'plaks' meant to be hung in one's room, locker, etc. Each long vertical card featured a hole near the top that was perforated so that it could be punched out easily, and thus the card could be hung on a doorknob. Each one was some variation of a Keep Out or Out To Lunch sign, featuring such slogans as Beware Vicious Dog and Danger 45,000 Nuts! with appropriate humorous graphics.
Note: two cards came in each 5-cent pack, but were attached as a small folder, which had to be opened by pulling a small tab. Thus, 'mint' Crazy Hang Ups cards must still be in their unopened, attached state.