These two Sumerian cuneiform characters stand for "Ama-gi"; literally "return to the mother (ama)". According to Samuel Noah Kramer, they can be interpreted as the first known instance of a term that we can translate in our language as "freedom".
Understanding the meaning of a concept developed thousands of years ago is always risky. But, if we think about that, freedom and slavery are closely related concepts and, as pointed out by David Greber in his "Debt, the first 5000 years", freedom means first of all "Redemption," the action of periodically erasing all private debts.
It was an idea, probably, developed first by the Sumerians, who had developed a sophisticated economy - even though they didn't have what we call today "currency". They also must have understood that in a finite world there cannot be such a thing as infinite growth, which is the way compound interest works: it grows forever. Hence, the need for the Ama-gi; the periodic erasure of debt and, as a consequence, of slavery. An idea that was maintained by the Jews with the name of "jubilee".
Apparently, in our age, we are so dazed by the concept of "economic growth" that we cannot imagine a world in which the economy (something real) can't grow as fast as debt (a purely virtual human invention). So, we are willing to sacrifice everything to a mythical and impossible growth, even at the cost of becoming all slaves.
According to Wikipedia, a number of libertarian organizations have adopted the cuneiform glyph as a symbol. It is used as a logo by the Instituto Político para la Libertad of Peru, and another version is a trademarked logo of the libertarian publishing firm, Liberty Fund.