By Joanne Babbage
Business reporter, BBC News
Coca-Cola is sponsoring the London Underground licensed busking scheme
"Ain't singin' for Pepsi, ain't singin' for Coke. I don't sing for nobody, makes me look like a joke."
So sang Neil Young on the title track of his 1988 album This Note's For You.
There used to be a time when no self-respecting musician would ever bow to corporate pressure and allow their songs to be used to advertise products.
Those days are definitely over, and never more so with the news that Coca-Cola is looking at "incentivising" buskers on the London Underground to include its Holidays Are Coming jingle in their repertoire over the festive period.
Coca-Cola say they won't be forcing anyone to sing the jingle, but if any of the buskers take up their offer you could be hearing that tune from the end of November, as part of the company's sponsorship of London Underground's licensed busking scheme.
But if you think this kind of advertising is unusual, you will be surprised to hear that it is already happening.
In the USA, Unilever's Lynx male grooming line, targeted at young men, is known as Axe.
To introduce a new deodorant that smells of leather, called Axe Instinct, Axe sought out 20 street musicians and college bands in several US cities, using social networking sites like Craigslist and MySpace.
In exchange for upwards of $1,000 (£596), Axe asked the musicians to put up "Axe Instinct" signs, offer free deodorant samples to passers by, and include a jingle entitled Look Good In Leather that Axe is using in its commercials, in their usual song list.
Sponsored busker in New York's subway
The scheme started in September and will run through to the end of the year, with some participating musicians playing on the New York City Subway.
Kirk Hullis, an account director with Rubber Republic, a specialist viral and social media agency, thinks it's a great idea.
"Using ad money to pay for something that will, in theory, brighten people's day with no strings attached is great," he argues.
"With all viral advertising, you have to use the money to give people something that they want or will find brilliant, so they feel warmth towards your brand, rather than feeling that they are being sold to."
A recent study showed that the amount of money spent on online advertising in the UK has overtaken that for television for the first time.
Viral advertising has come to describe any piece of advertising that people feel compelled to eventually share with their peers online, which spreads by electronic word-of-mouth.
The theory is that online views for the advertising grow as it is passed on, in the same way that a virus would spread from person to person through a population.
Viral marketing is comparatively cheap. According to Mr Hullis, a £60,000 budget can get you more than two million confirmed "engagements" with a brand.
This type of marketing is very accountable because the company can measure how many clicks it has had, how long people have spent looking at it and which sites it has been forwarded to.
"Advertisers love this. They love the fact they can get their ads featured on sites where they might not ordinarily have been able to afford to," says Mr Hullis.
"For example, advertising on Facebook is pretty minimal, but if you can get people watching your film on Facebook and sharing it with each other then you'll get thousands of views," he says.
In August 2007, Cadbury's aired a 90-second television and cinema advertisement which cost £6.2m to make and market.
The ad consisted of a gorilla playing the drums along to the song In The Air Tonight by Phil Collins.
Shortly after the commercial aired it was uploaded to the video sharing website YouTube and viewed over 500,000 times in its first week.
Phil Collins was played by a drumming gorilla in the Cadbury chocolate advert
By November 2007 it had been viewed more than six million times and shared across a large number of other video sites.
The drumming gorilla had 70 Facebook fan groups and the ad was even parodied by Wonderbra - the tagline "A glass and half full of joy" was replaced with "Two cups full of joy".
Even Pudsey bear was seen to ape the gorilla for the BBC's 2007's Children in Need fundraiser.
Because the advert originated on TV some purists will argue it isn't viral, but what happened after it went online goes to show why advertisers think the internet is now so important.
Other campaigns which originated on the web include T-mobile's karaoke session in Trafalgar square, which then became a TV advert, Volkswagen's subway staircase in Stockhom that was turned into a piano and Samsung's sheep covered in LED lights.
"Given the large amount of viral content around these days, ads that go truly viral, and spread like wildfire under their own steam are not as common as they used to be," according to Mr Hullis.
And intense competition amongst businesses to come up with the next big thing is good for the industry, he argues.
Peter Murphy busks as a harpist on the London Underground
"What it is doing is making companies look to do more and more innovative stuff within this area of advertising."
As well as the busker sponsorship, Coca-Cola's Christmas campaign also includes TV and billboard adverts, as well as on-pack promotions.
The brand's website Coke Zone will be offering daily prizes and will run a radio partnership with Capital FM in December.
So, the company seems to have all its advertising bases covered, but one question remains - will they actually "incentivise" any of the London Underground buskers to agree to sing their jingle?
"If you dangle a carrot in front of a musician they'll take it. They need the money," says Peter Murphy, a harpist and licensed Underground busker.
"If this comes in then the busker is being used as a puppet to a capitalist system where someone is making more money than a busker. That's wrong. It's exploitation."