Opinion: in this week's column Sam Jacob argues against what he calls PRotest, proposing that new forms of outcry through marketing and the media are confusing and "only make us more alienated".

An episode of television show Father Ted called The Passion of Saint Tibulus sees priests Ted and Dougal protesting outside a cinema holding placards that read "Down With This Sort Of Thing" and "Careful Now". They're there, reluctantly, protesting at the showing of a film banned by the Vatican but through some loophole shown in their parish on Craggy Island.

It's funny partly because of its satirical jibe and partly because of the perplexed and hangdog expressions of the priestly pair. But I think its real comedy, the thing that makes that synaptic spark pleasurably jump across the tracks of your neural network, is how it plays with protest as a form. It’s the gap between the form (protest) and the content (vague, unspecific colloquialisms) that generates the joke. The form of the placard against the un-slogans they contain, the rhetorical high of "Down With" finished by the pathetic "This Sort Of Thing".

Traditionally, the form and content of protest were one and the same thing. You could march on Aldermaston to ban the bomb, you could camp outside Greenham Common in protest of American nuclear missiles being based on UK soil. You could sit down in the path of a bulldozer about to demolish whatever it was you didn't want it to demolish. You could stop trucks transporting whatever it was you didn't want transported. You could march against a war, a policy or an ideological position. You could protest about a thing you disagreed with. You could say what was wrong with it. Sometimes you might even say what you would rather happen. The message was communicated by the action. The action was dictated by message. And of course, these forms of protest still happen.

But staring at an image on the Daily Mail website, it struck me that contemporary forms of protest have developed an altogether different relationship between form and content. It was an image of a child’s passport picture with the word "Help" etched in blue biro stuck onto Constable's The Hay Wain. The image of the child had been pixillated by the Mail and the background of Willy Lott's cottage was a blurred blow-up of a jpeg, which only made the whole thing weirder. The story reported a statement from Fathers 4 Justice saying that the act was a protest, a "final act of desperation" after a man lost a final appeal in the High Court over custody rights to his son.

Here the action and the cause are entirely divergent. It is essentially a garbled succession of signs and symbols. The Hay Wain is the apparent site of the protest but the protest is nothing to do with the art, nothing to do with the painting’s role as an icon of Englishness, nothing to do with what Constable’s picture shows, nothing to do with the landscape of Dedham Vale that it depicts. Its only role in this protest is the celebrity status of the painting, perhaps its insurance value too.

The child's image isn't placed into the picture as part of the picture plane if as by a collagist (like, say, a moustache on the face of the Mona Lisa - despite the potential for a bobbing child in unexpected depths of the River Stour). It's stuck onto the surface of the picture as though Constable's canvas were as undifferentiated as a pinboard. There is absolutely no reason why the head of a real-life, modern child is set adrift in a nineteenth-century pastoral landscape.

There are a myriad of potential political meanings inherent in the act of defacing a national treasure. Which one? How? One might consider the way the "which" and the "how" connect to the matter in hand, but here this is all ignored for the simple fact that the act would be mediated, that it would feature on the Mail (and many other places). Its site wasn’t really The Hay Wain or the National Gallery, but the media. Some might describe this as savvy. I think it's something else: a meaningless semiotic jumble of symbols with all their meaning sucked out of them, an unintelligible babble of references that are as unreadable as they are recognisable. In other words, its a form of postmodern protest: floating signifiers with a cause.

Talking of protest and floating signifiers, take the case of Trenton Oldfield. Half of the duo behind This Is Not A Gateway (who create "platforms for critical projects and ideas related to cities"), Trenton infamously swam into the midst of last year's Oxford and Cambridge Boat Race. The act was clear. A perfect disruption of a media event guaranteed to get coverage. But his motivation was a murky as the river itself.

Was it about the boat race itself? Was it about elitism in sport? The elitism of universities as centres of excellence? The education system as a whole? The use of the river for a corporately sponsored sporting event?

At times it seems to have been about all of these things. The rambling, unfocused justification posted on the internet seems to have vanished. Now, post-incarceration and with an application for a visa turned down, it seems the act has multiplied its potential meanings, both for Trenton and for those who keep one listless eye on Twitter for things to get momentarily excited about. The act of jumping in the river now holds fleeting meanings about the establishment in general, judiciary, prison, the state of television or colonisation, depending on which interview you read. The original act gathers meanings like a snowball, only for them to melt as fast.

I'd argue that the fact that there seems to be no single point is the point. The act and the subject of these protests have become delaminated. It's as though any subject can be attributed to any act, and the interchangeable relationship between the sign and signified makes it a postmodern form of protest. Doubly so, because the shifting arrangements of form and content take place within the media - in the representation of the act, not the act in and of itself. It's protest by way of marketing, PRotest, to coin a phrase. The worry is that by operating as a form of marketing, this kind of protest only serves to reinforce the mechanisms of contemporary society, only makes us more alienated, further from a position where we might be able to achieve anything.

Perhaps this kind of non-specific protest is a function of our own era. Maybe it's just harder to pinpoint what exactly is wrong because, quite frankly, everything is kind of wrong and there's nothing anyone can do about it. Think of the Occupy movement, whose lack of demands and proposals were coupled with a raggle-taggle, multifarious collection of disassociated issues. Its real statement was just in being there, occupying space and column inches, and not really doing anything.

We live in an age where political engagement is increasingly reduced to likes and re-tweets. Meanwhile, mainstream culture continues to appropriate the form and aesthetic of protest for its own ends (what else is Banksy, for example, than the ultimate fulfilment of the Clash's lyric "turning rebellion into money"). This de-politicised addiction to form and sensation - rather than content - gives us the protests we deserve. As Dougal says, "Careful Now".

Sam Jacob is a director of architecture practice FAT, professor of architecture at University of Illinois Chicago and director of Night School at the Architectural Association School of Architecture, as well as editing www.strangeharvest.com.