Japanese symbols in nicknames
Signs like ツ, 彡 and 乙 come from Japanese and Chinese writing, but in nicknames they are used for their shape: ツ looks like a smile, 彡 like speed lines. They are real characters, so most games and apps accept them.
Kawaii faces and hearts
Kawaii faces like (｡•ᴗ•｡) and hearts like ♡ゞ suit bios and chats. They are long, so in game nicknames use a single sign such as ツ or 彡.