Mark Wallinger has always had an itch for public transport: witness Threshold to the Kingdom, filmed at City airport, or Angel, which featured the artist walking down a station up-escalator reciting St John's Gospel backwards. The 2007 Turner Prize-winner is also fascinated by signs and codes. So if anyone was going to make an artwork for each of London Underground's 270 stations, then Wallinger was he.
But first, Edward Johnston. In 1913, a square century ago, Johnston designed the Underground's red, white and blue roundel, a symbol now so familiar that it has become a metonym for London. Like Harry Beck's 1931 Tube map, the logo is misleading. Just as the Circle Line is not, pace Beck, neatly bottle-shaped, so Johnston's geometry and sans serif type suggest that travelling on the Underground will be a rational experience. This is not borne out in fact.
Which means that Labyrinth was a pretty brave commission on the part of London Underground Ltd. Among Wallinger's better-known hobby horses are myths and the debunking of them. A logo that has both entered the national psyche and sets out to mislead it is the kind of thing to set him licking his lips.
You can see the outcome of this at 10 Tube stations so far, including Oxford Circus. Its personal Labyrinth arrived on a wall a couple of weeks ago, between a ticket counter and an Oyster card machine. I imagine most of the quarter-of-a-million people who surge through the station each day haven't even noticed it; they may never do so. The only thing to suggest that it is an artwork rather than signage is that it bears a discreet number, 60/270.
That secrecy is very Mark Wallinger. Like all the others, the Oxford Circus Labyrinth is a circular composition, black on white and about the size of a Johnston roundel. You vaguely imagine tourists scratching their heads at it in a sad-eyed attempt to find Fortnum's. It is a graphic maze, like the ones children trace their way through in comics. At its entrance stands a little red cross, jaunty and hopeful. It seems to stare at the maze with a question-mark over its head. You Are Here, it says: but where are you?
And what is this Labyrinth? Good question. Johnston's roundel was the visual abstraction of a set of ideas – logic, modernity, speed. Wallinger's is, too, although his ideas have more to do with Homer and Barthes. Like Daedalus, the Homeric character who built a maze for the Cretan minotaur, Wallinger is an artist. You sense his identification with the man who, in Ovid's telling, made a labyrinth so cunning that he was almost trapped in it himself.
Wallinger's labyrinths are also quietly subversive. Part of the way artworks control us is in insisting on how we look at them. Michelangelo's David demands to be seen in the round, while we have to squint at Holbein's Ambassadors sideways-on to discover the picture's anamorphic skull. To find our way through the Oxford Circus Labyrinth, we would have to stop and trace a path with our fingers. Try doing that in the rush hour. If Johnston's roundel called out to the conscious mind, Wallinger's whispers to the part of it that fears tunnels and the dark.
Something else strikes you about 60/270, particularly when seen in the company of its friends, 142/270 (Bank) and 101/270 (Westminster) in a show of artworks from the LUL commission at the Anthony Reynolds gallery, a short step from Oxford Circus. Johnston's design set out to integrate, to show the Underground as a unified network. Each of Wallinger's labyrinths is different, although that doesn't mean we can use them to navigate by.
Rather the opposite. There is, intentionally, no sense of place in his system, nor – short of Wallinger spending the rest of his life travelling to 270 stations and getting to know their different locales – could there be. No, the point of each Labyrinth is that it is a symbol of itself, or, rather, a symbol of symbols.
There is something faintly Dan Brown about all this. Conspiracy theorists will recall that red, white and black roundels incorporating a cross were used to some effect by the Nazis. Reducing things to symbols, as Wallinger is aware, is fraught with danger. His labyrinths remind us of that.
To 27 April (020-7439 2201)
There's double exposure for Man Ray, with two exhibitions of the Surrealist's photographs in London. The bigger is Man Ray Portraits at the National Portrait Gallery (to 27 May), focusing on his work in America and Paris, where he snapped friends, colleagues and lovers. Shown in tandem at the Atlas Gallery, Man Ray: Contacts affords greater insights into his work, incrluding raw, untouched versions of famous images (until 30 Mar).