What is the name given to the process of signaling with hand-held flags?

Phew just got through level 666!!!!

Level 1,127 here...

luckycatfay, at 409 here.

That’s same as for planes on runway, buses and trucks in parking garages and equipment movements on construction sites. ! ! !

Level 314 for me. Nice to know I can be playing a long time! 😃

level 786 here at this question.