We have made a series along Post Road with a "Post" theme.
Post (verb): 1. to stick or pin a notice on a wall in order to make it publicly known. 2. internet and telecoms to publish something such as a message or picture on a website or using social media.
Now doesn't a combination of 1 and 2 describe a geocache? Although the message is often not out in the open and viewable by muggles.
Experienced geocachers will have this one spotted from the road.