to do something to show that (a day or an invent) is important or an occasion for rejoicing

commemorate occasion, achievement

to show or mark (something) in a special way

typify, distinguish

to identify, state, a difference between people, things (by looking, listening, thinking etc)

tell the difference

the system (code) for sending signals, e.g. by using one's arms or flags held in the hands, with various positions for the letters of the alphabet

indicate; give a sign to