I have never seen or heard of a method that tells 100% wheter it's a male or female. Only a DNA tester can tell that, but we pigeon fanciers always try to guess what our pigeons are. I've heard multiple systems like
1. A female squab have taller yellow hair and the middle finger is taller than males middle finger.
2. You can tell from the colour that the squab have. Look at his parents and see their colours, then you may determine the squab sex. Though you need to find a genetic expert.
3. And this is the sytem that I use. Look to it's head and see what shape has. If its round then it's a male and if it is flat its a female. Altough its not 100% as a female can have a rounded head and viceversa.
I'll post pictures soon! As now the camera is broken :/