Do Fighters/Trainers have secret signals?

First of, I must say I'm very proud of Brook's performance yesterday. Didn't expect the fight to go the distance, but he showed guts and skills while it lasted, props to GGG. Now onto the main point, do Fighters have secret signs or signals to tell the corner to stop the fight?? When it became apparent that Brook's eye was troubling him, Ingle whispered to Kell when he was sat on the stool. A round or 2 later, as soon as Brook gave the "Is that all you got??" Showboat with his arms in the air, his trainer immediately started to wave the towel. To me it seemed like a secret signal to his corner to stop the fight.