The origin of the symbol used by squatterz today is somewhat in dispute. Much like punk rock itself, the symbol started appearing sloppily drawn, and neatly stencil-bombed on walls on the streets of both London and New York in the mid to late 1970's.
Though squatters have existed since the first caveman moved into his digz and pissed on the wall, it had primarily been an act of necessity as the population of local poor, migrant workers, hoboes, gypsies, and traveling con-men/ criminals appropriated abandoned buildings as their dwelling places.
It was not until the mid 1960's that mostly upper middle class white idealists and activists began squatting the neighborhoods in order to escape the oppression of landlords and taxes and set up communal living arrangements where they could exist in temporary autonomy free from hassles by "the man."
Hence what was originally an act of survival became an empowering political statement. Through their lifestyle, these young people were pointing out, (and taking advantage of) the urban decay in our inner cities, as well as protesting greedy landlords, outrageous rents, gentrification, and illegal eviction.
When A.I.M. and the Native Americans squatted Alcatraz in the 1960's it was a big middle finger in the face of a government that had murdered, ghetto-ized, and oppressed their people for years.
Whether it was the gypsies and tinkers of England and Europe or the Hobos of the U.S., travelers have always had a "secret language" of signs and signals. The roots of this language can be traced back to early Christian times, (sometimes called the Burning Times) when Pagans used symbols to communicate amongst each other and to plan their illicit worship right under the watchful eyes of blood thirsty and over zealous missionaries. As any clever anthropologist could tell you, a pile of stones arranged by a field, road, or railroad tracks could tell a gypsy whether that field was safe to camp in for the night or if the farmer/landlord was likely to chase a "damn 'bo" off with rocks, salt and pitchforks.
A British tinker at the turn of the century could tell a lot about an empty building by the chalk marks scrawled on its outside walls. Sadly, most of this information is lost to us today.
The squatterz symbol as we know it today has been appropriated from the Nordic Runes. The circle "O" represents a womb or dwelling place and is pierced by "/", a rune known as solely representing power, (hence Hitler's use of the rune for his elite corps or storm troopers), or a lightening strike. To the ancient Vikings the rune represented divine inspiration! Wisdom brought to earth through Odin, the all-father or his son Thor, (whose special province was lightning.)
The arrow coming off the top of the lightening bolt is also a rune called Teiwaz which is representative of victory or the spiritual warrior.
Quite appropriate for a tribe of urban, nomadic hunter/gatherers, if ya ask me.
There is, I am sad to say, also a bit of East/West rivalry and dispute as to the proper depiction of the squatterz sign, as it first appeared in the WW2 comix in the mid 80's. One style is preferred by New York squatterz with their roots in L.E.S. West Coast punx, (who tend to be more PC as a rule) seem to have altered the symbol slightly so that part of it stands for womyn and Omen living together in equality.
And there ain't a damn thing wrong with that.