I'm using textual labels for three buttons:
- Legend - this is pretty unique to this site, and I can't think of a universally understandable icon. I'm pondering whether Legend deserves to be a top level item or should be under "?". I also hide Legend on small screens.
- Important - this is a "default" search for important worlds. Again, no universal icon for this concept. I believe this feature will evolve into more of a "browsable, sharable sets of points of interest". Maybe a point-of-interest icon, then?
- Share - this one is starting to shake out as a standard icon - the three circles in a < formation - but it's not quite universal yet.