What is an AM?
As long as the father does not have a gene for barring/cuckoo then all male chicks will hatch with a white spot on the tops of their heads. As long as the chicks surrounding down color is dark enough (not white or light yellow) then they can be identified. The white underbelly, neck, cheeks,and wingtips are typical of the E series genes which include blacks and birchen.. You only look at the top of the head for sexlink characteristics.
Included are pictures off my black sexlink project, lavender Ameraucana over BR and cuckoo marans..my lavender Ameraucana has a gene for black and a gene for birchen (I rest bred him before the project so I would know what to expect)