I just hit the absolute jackpot for information on symbols online. People who are into this stuff are going to cry when they see this site. It’s called Glyphalia. Here’s a sampling of their link categories:

• Information Processing and Software Development
• Natural Languages
• Mathematics and Science
• Business
• Space, Military, & Maritime
• Art & Entertainment
• Fonts & Typography
• Cultural and Political
• New Age and Occult

Unfortunately a lot of the links listed seem to be broken, so you may have to dip into the Internet Archive or Google’s cache. But still a great find nonetheless.