Signs blank out seemingly randomly when typing text

When I type in signs, there are some bizarre things the system forbids me from saying. My specific issue is that I am trying to create road signs that point to mine and my friends' houses.  For example, if I type in "Kaitlyn's House" the system works fine. But if I type in "<-" in the first line (an arrow), and "Kaitlyn's House" in the second line, the entire sign goes blank as if I entered a censored word. Am I doing something wrong? This seems like a stupid flaw in the already ridiculous censorship system.