I imagine given the engine wasn't designed with this feature in mind, that this may be too difficult to implement, but...
It would be really cool if one could build trade shingles and hang them off signposts or buildings. A trade shingle is basically a carved wooden plaque with a recognizable image on it, used in period to designate trade shops to a largely illiterate public. This would require adding a new interface meme, the idea of "modifying" an existing structure. Personally I envision this being a right click option on a structure bringing up a set of mooring points where modification was possible, each mooring point having its own set of recipes (potentially).
In-game, a trade shingle would just add an image (depending on the shingle made), that would hang by the door of whatever building it was attached to (shed, townhouse, etc.). The signpost would be just that, a post.. with a shingle (or the ability to add a shingle). Shingles could be put up with the recipe (Any Shingle, 2 wooden plugs).
They could be made with whittling (or maybe a skill off of whittling if one preferred). A set of 10-20 trade symbols would be sufficient (metal, crops, meat, the shroom/plant symbol, fish, leather, brick, weapons & tools, lumber at a minimum). If one wanted to go crazy, you could make it a two part process, in the first part you'd carve the plaque, which would allow you to choose from a few different shape/styles, and then you would carve the symbol. I'd settle for one step 8).