I have seen the belly rub also the hands in fists with thumbs up being brought to your mouth like your shoveling in food for beans.
Head in a siding tapping your head ,back in tapping your tush.
Slow was a slow flaping motion like "easy does it" you just made your hands go up and down at your sides like a bird. It turns into a stop signal real easy.
Kick I have seen done just by kicking with a foot holding up a fist with how many ever fingers was how many you wanted to kick so the engineer could wind her up tight or not.
Washout a REAL fast stop.Like oh crap the new hire forgot the derail!!!!( I have seen people almost fly with this one
We had a guy telling roundhouse stories one night. he gave the signals all right down to the joint then signalled "Going between to couple the hoses" as he was attempting to do this another switchman grabbed him pulling him back just as the cars were moving! Seems that signal was ok for his home yard but here it meant "shove em pin didnt drop"
Signals were different from road to road and terminal to terminal. I agree why ues a radio when running light! Plus with hand signals your progress cant be monitored by all in ear shot so to speak. You get the work done a bit earlier you go to beans longer. Or if your just having a real crappy day no one needs to know but you and your crew.