Pinprick code hides the secret message in a seemingly ordinary letter/message. Letters from the secret message are marked out by placing a pinprick underneath each.

A dot below each letter can work as well if you don't have a pin. You just have to make sure that all the letters you mark out with pinpricks are in the right order for your secret message to make sense.

Example:

Someone leave a bouquet of flowers on your desk with a card in it. What's written on the card?

A vengeful soul is like a lighted candle,
                      •  •                                      • •
it can't hurt you if you'll stay away from it;
     •                  •                       •         •          •
but the one who started the flame
                                    •                       •
should be cognizant of its danger.
•               •                                         •

from: stuck_n_silence
               •

You didn't know what it means until you notice the pinpricks underneath some letters. You smiled after getting the message.

Hidden message:

Sunday_two AM_See u...