Awesome

sublime-opal

Syntax definition of the Opal programming language for syntax highlighting in Sublime Text 2.

How to use

cd ~/.config/sublime-text-2/Packages/
git clone https://github.com/artifactz/sublime-opal.git Opal

Then in Sublime Text you can [Ctrl]+[Shift]+P

Set Syntax: Opal

whenever you want. Opal files (*.impl, *.sign) are being recognized.

Sublime Package Control

You can make your life easier using Sublime Package Control and get updates automatically.
If you've got it installed:
[Ctrl]+[Shift]+P

Package Control: Add Repository

and use this site's address: https://github.com/artifactz/sublime-opal
Then [Ctrl]+[Shift]+P

Package Control: Install Package
sublime-opal

Please note that the manual setup and installation through Package Control are XORed. Doing both results in two distinct installations of OPAL syntax highlighting, which probably is not what you want.
If you're using a manually installed OPAL highlighting and want to try out adding it through Package Control, please delete ~/.config/sublime-text-2/Packages/Opal first.