Shape is nearly universal (a red octagon) -- the real tell is which word is written on it.

Shape (a downward-pointing red-and-white triangle) is standardized almost everywhere -- text and border details are what separate countries.

Shape, material, hole patterns and paint details on utility poles vary a huge amount country to country -- one of the richest meta categories.

Roadside reflector posts are one of the most reliable GeoGuessr metas -- shape, color, and reflector placement differ sharply by country.