How you let someone know that you have a crush on them?

Talk about him/her with your friends when he's close by.

Leave little hints like asking him if he wants to go to the park or movies with you and your friends. Soon he should ask you out!

or

YOU SIMPLY "LET" THEM KNOW.

(Direct communication is the way around finding another way around communication)

If the crush is reciprocated only after a masquerade of subterfuge and the engendering of delegate cupids, then the relationship might be a mask, and the face value is unpredictable.

Go ahead, or raise your tail.

You call it.