I know the US posters on this site find some of our weapons laws in the UK pretty laughable. While I am quite happy to accept restrictions on sales and carrying of various dangerous items, I admit seeing this poster in my local shop nearly made me drop my biscuits (not a euphemism btw)
As it's come out quite small I'll elucidate - no sales of eggs or flour to unaccompanied under 18s in the period coming up to Halloween and Bonfire Night (November 5th)
Further information here.