420 is a non day holiday for all the pot smokers of the world. Originally, it only referred to April 20th which some how, from someone(s) became the official unofficial day of staying high, not that many in that sub-culture need a special day to be stoned, but... As time progressed, it went from April 20th to any time frame which included the numbers, "420," as in 4:20 PM.
320, thus becomes an hour early. The reality though, is that I saw the neat sets of lines and that's what first drew my eye. Left verticals, right horizontals with two intersecting diagonals to break both planes into manageable areas of visual inspection. I really liked how the wood door and galvanized corrugated metal almost became one surface after years of painting, repainting and lots of rusted surfaces. 320 is just the street address.