Almost everything geospatial deals with symbols on maps or other types of displaying mechanism. Here's a new source of symbols coming from the OGC MetOcean DWG, the 'World Weather Symbols' available on GitHub.
It is described as "A complete set of WMO weather symbols in SVG with full metadata." It's not a version 1.0, but they are fully usable right away and there's "A set of pre-generated PNGs are available for download […]". From the same source you can get the 'World Meteorological Organization - Regional Associations' (WMO-RA) in geojson, which is vector data representing the "Six regional associations are responsible for the coordination of meteorological, hydrological and related activities within their respective Regions […]".
Other openly available geospatial-related symbols sources that I'm aware of include:
- Maki icons - open source pixel-perfect icons for web cartography
- Emergency Mapping Symbology - from NRCan's GeoConnections
- GLYPHICONS - while not specifically targeting mapping, the free section is Creative Commons licensed
Any other pertinent source?