Not necessarily for haircuts, but for tax-free transactions, find a CPA, preferablly versed in Austrian Economics.
The backwards dollar sign is used by people around here, I don’t know how widespread it is.
There are also the libertatis aequilibritas:
The voluntarist “V for Voluntary”:
The anarcho-capitalist banner:
The emblem of the Alliance of the Libertarian Left:
Also suggested are the Gadsden flag and the Jolly Roger.