They look a little bit like alien crop circles marked on the asphalt; some kind of secret code that echoes the constellations and the carvings of ancient civilisations.

If you've walked around Melbourne's inner north recently, you've probably seen them painted on footpaths near tram stops, gutters and street signs.

One of 'countless' Astral Nadir drawings. Credit:Instagram: @astral_nadir

In a city where the walls, fences and alleys are a rotating canvas for an endless supply of street artists, the ground is left mostly untouched by spray cans and paint brushes.

Perhaps that's why the subtle white pavement drawings, which are the work of an artist known as Astral Nadir, tend to stand out. After you've seen one of them, they seem to pop up all over the place.