What is the best way to mark it?
Do you use a coin or the chalk cube or something else?
Should you call it and mark it? What if your opponent is too busy doing something else to pay attention and not look you in the eye and confirm your call?
I have had this happen in bars many times.
After an honest, but unsuccessful attempt to get my opponents attention to confirm my call, I will often see if one of my opponents friends or acquaintances is paying attention and let them know what my intended pocket is. I suppose that person could deny that I called the pocket. It might be a better idea to let one of my friends or acquaintances know what pocket I am shooting at.