Can anyone help this noob shine some light (pun intended) on the situation?
Not a hope in hell, given ONLY the information you've provided so far. Which is ALL the information we have.
Re-read your post. Imagine some of the things that you'd need to explain to your grandmother. Like what the hell Pro Tools is, and how the Arduino would have a clue that you pressed some icon in some application running on some PC somewhere.
Like HOW the Arduino is connected to that computer.
Like what code the Arduino is running.
Like what pin(s) the sign is connected to, and what is actually between the pin(s) and the sign.