Do whatever you can; usually the school has a bulletin board for such items. While not be a great attention getter from the kids’ point of view, some parents actually do look at the bulletin board, so it’s an opportunity.
On JSN during the morning and afternoon carpools, you can also have volunteers holding JSN TONIGHT posters. Morning carpool may be the best opportunity as most elementary schools have dismissal time down to a 7 minute blitz! Be sure the posters have printing large enough to be easily read by drivers going by. See additional discussion on activities during the day of JSN below.
In addition, consider placing posters in local community friendly places such as the library (if they will allow), grocery stores, independently owned or franchised pizza or hamburger restaurants, toy stores and other such retail establishments. Many of these places will tape your poster to their window, so you may want to have it dual sided so it can be read from inside and out! You can use the official BSA posters, make your own using basic poster board, or there are even some software programs that allow you to make a poster sized printout by using four 8.5 x 11 sized “labels” and then sticking these “labels” on a poster board backing.