Incomplete List of Annoyances (Part 3)

In which The Author sees an irritating use of English

Signs that say things like ‘Opening Hours 9 a.m. – 12 p.m.’
You see them on the doors of pubs, supermarkets, and clubs. Quite often, the same misuse occurs on posters for gigs and nightclubs. The reason these signs get my back up is that there’s no such time as 12 a.m. or 12 p.m.
My friend James E. and I were talking about this at his graduation a fortnight ago. He’d noticed that the police station near his home is (apparently) open until 2400. He asked me if there was any such time. Well, of course there isn’t.
Just before midnight, a radio-controlled digital clock (such as the one on my bedside table) will display 2359:59. Once the day ends and the new day begins, the clock changes to 0000:00. Anyway, I’ve just come across a poster for a gig on Facebook, and it’s reminded me of our conversation.
As Prof Jim Al-Khalili would say, let me explain:
a.m. is Latin for ante meridiem – which means ‘before noon.’ Similarly, p.m. means post meridiem – ‘after noon.’ And the time in between is noon. Not morning, not afternoon – just noon. Twelve hours later, it’s midnight. It’s not 12 a.m., or 12 p.m. – it’s just midnight. It’s not rocket science. Please, please, stop doing it!
Thanks for listening.