You can always go with an element or a planet. Something with a common name, like how we are Team Mercury. Sometimes we play up the planet Mercury and space like we have the past few years, other times we play on the element mercury and its chemical symbol Hg (aka quick silver, which we've used for our robot names) and still other times we've played off the Roman god Mercury, the messanger. It makes it fun to be able to switch it up. Also, your theme and logo don't really need to match I mean, we have a lightning bolt cause it's cool.
