Allow signposts to be built on map

Building a signpost would allow a short text label to be set at a position on the map
Then whilst browsing around the map, if you hold down ALT (or toggle it with some hotkey/setting) it would show these text labels, aswell as larger production icons for each building

It should come with an area marker for marking parts of the map.

A bit like a region area on the map? So you can say brick works, steel works etc - easier to find when zoomed out :)