tell by
tell (someone or something) by (something)
To be able to discern or identify someone or something by some trait, characteristic, aspect, etc. You can always tell tourists by their big backpacks and tendency to photograph absolutely everything. I could tell by the style of film that I would really like it.
tell someone or something by something
to identify someone or something by something. You can tell Jim by the old-fashioned shoes he wears. I can tell the new season's fashions by how short the skirts are.