Adding a geolocation to a post / page was introduced to the WordPress OSM Plugin many years ago – there are sites like Fotomobil.at and Hamburgs Brücken wich use it with hundreads of geocoded posts. The latests version of WP OSM Plugin added a sidebar widget at your edit post area to directly set the geolocation without dealing with custom fields by yourself:
If you want to, there is also the possibility to define an icon to the post which is later on shown in the overall map.
Beside the geolocation widget the latest version brings also some new icons, find them here.
And many thanks to Andrea for italian tranlsation!