When we need to get a minor message out, we sometimes put fliers in the common areas- laundry room, by the mailboxes, etc.
BUT- for retention, I make the effort to go door to door to ensure that my residents know I REALLY care about them. If money is tight, print the notes half-sized, two on one sheet.
To save time, I do it tag-team style. Put all the notices in a messenger bag, one person carries the bag, another person carries the tape. I hold the notice on the door, My assistant sticks on the tape, then he tears off the next strip of tape while I get out the next paper while we both walk to the next door.
We make sure to do mass posts when we wont encounter a lot of residents who will stop us with questions. We can post 100 notices in less than 15 minutes!