I usually get real silent and then slowly pick back up as I walk away; trying to whisper to myself and keep my voice low in case someone else is on the trail.
I don't think I've ever encountered someone else doing this .. except sometimes for that crazy homeless person on the street .. and they don't exactly stop when people walk by them.
I've started to think I'm probably one of the few people who do this, but it's so helpful to hear my thoughts to put things into order and organize them that it's not something I really want to stop doing.
I also talk things out while driving alone. I used to get embarrassed that other drivers could see me. But now a days hands free phone systems are commonplace in cars so I just talk away :)
Nice hint. Gotta buy a highly visible bluetooth headset.