Earlier quoted context omitted.
Indeed. This one used to mystify us on the UK driving test 25 years ago - way older than steam trains, and presumably anachronistic even when it was standardised: http://wwwdelivery.superstock.com/WI/223/1848/PreviewComp/Su... It's not a UK sign. Most Europeans will recognize it, but I doubt it travels well, and even where it has local currency, many peoples grandparents won't remember these in real life.
I recognised that one as a horn, but I had no idea what the connection to post is, and still don't. Just took it for one of those weird corporate logos that meant something to someone at some point but doesn't anymore.
http://en.wikipedia.org/wiki/Post_horn
The post horn...used to signal the arrival or departure of a post rider or mail coach. It was used especially by postilions of the 18th and 19th centuries...The instrument is still used as the logo of national post services in many countries.
The logo I posted was for the German mail service, but you'll see variations of that image used to mean 'post' all over Europe, and in Australia.