I think that this symbol implies that there is a post box and/or post office here. This was closed some time ago and the post box and post office are at the Bell House Hotel

There are two amenity=post_office nodes one on each side of the road here, and one of them has a ref=* value that looks like it should belong to a post box.

Presumably there's should be one Post Office and a post box here in reality. Needs a survey.