I'm reading through the book now and the besides the signalling vs human capital argument the most interesting part is how he breaks down what college students are signalling into 3 parts that companies are interested in.

1. Intelligence - By passing tests 2. Conscientiousness - By doing it for 4+ years 3. Conformity - By not figuring out a way around it

It's an interesting exercise to think of how different careers might value these 3 factors plus human capital differently.