Generally, sites with the beta theme get their initials in a cartoon question bubble. The primary reason is that we create several sites a month so we need an easy-to-produce design icon consistent with the beta theme and the other sites on the network. If you look through the list of sites, you'll notice the occasional beta favicon that's not in the Latin alphabet. (By my reckoning, that includes Anime, Arduino, Aviation, Chess, LEGO® Answers, Poker, and Puzzling??) But all those symbols are Unicode glyphs.
As pointed out in the comments, Craft CMS has a custom icon. (That's not without trouble of its own, however.) To give you the back story, shortly before private beta, the company behind Craft CMS contacted us with a complete set of icons which they graciously gave us permission to use. It wasn't really a partnership since we hadn't heard from (or, in my case, of) the company before the proposal was submitted to Area 51. We didn't go asking for it. We also would not have considered using the icon if it were not the logo of the product that makes up 100% of the topic space of the site.
If you found a Unicode glyph that unambiguously expressed "Robotics", we would consider changing your favicon. But I think your efforts would be better rewarded if you focused on increasing participation on the site. Name and icon changes have historically made little measurable impact on the activity on a site. We are still trying to figure out what can be done to propel a site from a solid, but slow beta to graduation. One thing I'd like to suggest is a weekly topic challenge.