Personally, I would not confront someone (strangers) who are talking loud on their cell phone. Many times they are aware they are talking loud, and simply do not care. If possible, I would move away out of hearing distance from them. If that is impossible, I would just ignore them as much as I could. Eventually they will walk away, or get served in line and leave. Regarding giving hand gestures to indicate to someone they are talking loud -- depending on their mood, they may become upset and retaliate by talking even louder. In my opinion, it is safer and non-intrusive to move away, or ignore the loud, impolite cell phone user. I may not be able to control the cell phone user talking loud on the cell phone, but I can control how I react -- which is to get out of hearing distance, or ignore, until the loud cell phone user leaves.