I found this website which describes the gpx syntax:
The help for tag states:
Text of GPS symbol name. For interchange with other programs, use the exact spelling of the symbol as displayed on the GPS. If the GPS abbreviates words, spell them out
On another website where you can import a GPX file into Google maps, you were able to select a color (eg red) and symbol (eg triangle) for waypoints to be displayed on the map.
So I don’t see any standard definition, but using something like speaking color names like blue, green… and forms like triangle, circle or square might be common.
BTW, my idea was to create an overlay map with all mountain passes in one color eg blue, the ones I passed should be in a different colors based on describing how I personal liked them. This way I have an easy way to plan my next tour. I did this with Google maps before, but I thought it would be better to do it directly in kurviger instead. While planning my next route I can easily determine which mountain i did yet not pass and find the ones I liked the most.