Just to be clear, I'm not disagreeing with anything that Storm has said, but one should point out that the things mentioned above are by no means exclusive to CC3+, They apply just as well to MapForge and Fractal Mapper 8. All three programs use PNG graphics as symbols, so if you acquire a PNG symbol or make one, you could use it in any of the three programs. FM8 also includes ISO symbols for overland mapping in both its PNG and vector symbol sets. That doesn't apply directly to MapForge, because it works with add-in graphic packages rather than individual PNG symbols, however, one can import individual PNG symbols into MapForge.
There aren't any in Cosmographer either or anywhere else including RPGMapShare, as far as I know. I'm pretty familiar with what's on the RPGMapShare site, and I have Cosmographer. Cosmographer has mostly symbols for furnishing the interiors of spaceships and space stations in deckplan mode. It has planets and similar space objects in starmap mode. It has geographic symbolry and hexagon landscape fill stamp symbols in overland mode.
ProFantasy also has issued a few annuals with sci-fi tools, but I've never seen them, so I can't comment upon them.
The space/sci-fi part of the Dundjinni Archives, which are free in both CC3+ and FM8 versions and can be imported into MapForge, also has symbols for furnishing space ships and space stations in deckplan mode along with personal equipment and creatures. It has planets and a wide variety of spaceships in starmap mode. It has nothing in overland mode.
The Symbol Set 3 add-on for CC3+ includes modern symbols typical for the 20th Century. Things like computers already are outdated for the 21st Century.
For the record: I have licensed installations of MapForge with quite a few add-ons, Fractal Mapper 8 and CC3+ with the eight main add-ons, including Cosmographer and Symbol Set 3. I have mapping experience with all of them.
I find that strange too. FM8 is produced by NBOS Software. It's top-selling program is AstroSynthesis, which can work together with FM8. AS/FM8 users produce a lot of "how to" queries, but if they post their maps anywhere in the Internet, I have no idea where that is.