Poor Man’s Copyright for my Song

Being interested in music, I have been writing lyrics since my highschool days. Until now, when my mood strikes I write some lyrics. When I was out of the country years back, I was able to write a lyrics inside the four corners of my room. Maybe the cold weather outside took me to write one, the song is supposedly a sad song, but later on I finally decided to give it a twist with a humor on it. 

This song is one of my favorites I wrote so I decided to have a poor man’s copyright by writing it on a sheet of paper, put it in an envelope, and brought it to the post office addressed to my home address for whatever purpose it may serve in the future. I do not know much about copyright, this is the only way I know. When I arrived from my travel, the mail already arrived ahead of me. Until now, the mail that contains the song is still with me..unopened. I wonder when will it be opened.