As the parent of two teenagers who, like many of their friends, spend an enormous amount of time watching TV, I know that if you want to make them aware of something then your best bet is sticking it on the screen, preferably on MTV.
Simply putting up a few posters a week before the change is due to come in won't make a blind bit of difference to the people it is trying to target because I don't think they'll bother looking at them.
We've had posters up in the shop about the change for a couple of weeks now and the only customers to actually read them, I'm sorry to say, are the ones who are well over 18.
Retailers are well aware of the changes, but it seems that the public are not.
Where are the write-ups in the newspapers or the news bulletins on the TV about the subject? I expect they are hiding in the same place as the government's sympathy for us retailers who will get nothing but abuse from the 16 and 17-year-olds we've been selling cigarettes to so far this year.