Ok…, i was just listening to music while thinking about lucid dreaming and
was wondering if u hear music from say your radio while in a dream. 
If u can then you can probably leave a song on repeat of something
and train urself to recognize it in a dream. But then after thinking
about it it is just like setting a voice saying “I am Dreaming” in the middle of the night. 
And I would guess a topic like this has been made before. Sorry if it has.
Im to lazy to check. 