I've seen both "Chic" and "Tick" used for his name, but the strict romanji is "Chiiku" (チｯク) rather than "Tiiku" (ティク), so I'll defer to that.

Tick has a brother named Tock, so Tick would make more sense than Chic.

*snip*

I believe FUNimation's official spelling is "Chick", if that makes any difference.