In our mob, the minimum requirement is that there is one safety card per block of seats. It will be placed in such a position as to be reachable by anybody sitting in that block. Its precise position is not specified. However, the spec. given to cleaners is that there will be one per seat pocket. The seat contents will be arranged (furthest to nearest) inflight magazine, safety card and sick bag. We also carry spares of each - you don't want to be grounded because of memento hunters.
PM