While I won't directly take on your social signaling claim, there are some humanities which have clear utility (while also functioning as social signals), for example knowing the precise meaning and usage of a large set of words. People in the academy are not disdained for having this practical facility.
An adjusted version of your claim: I think that in some countries (including the U.S.) math & hard science are tarnished through their association with poorly-protected and therefore indifferently remunerated professions, such as accounting, pharmacology, and engineering. Most educated people I encounter would, all things being equal, like to be good at math, but some let themselves off a little easy. Trying and being bad at history would make you dumber than a lawyer, which feels okay; trying and being bad at algebra makes you dumber than an accountant, which is humiliating--so better not to try.