Next time you're watching a campaign rally for a politician, or a glitzy premiere, take a close look at the enthusiastic faces waving banners at the front. There is a good chance that some are paid performers. If they are, it is likely that one Adam Swart put them there. Los Angeles-based entrepreneur Swart has pioneered the 'supporter-for-hire' business. His start-up Crowds on Demand, launched in 2012, has established itself as a popular resource. The company repertoire has now expanded to cover product launches, PR stunts, and social justice movements. One popular side-line is using crowds to apply pressure to one side - or even both - of a corporate litigation dispute. Swart claims the business has more than doubled" in size each year, and can now call on tens of thousands of performers to cover several events each day, in dozens of cities across the US. "When a clients spends $10,000 on a protest and wins a $20 million settlement, that's a clear return on investment," says the entrepreneur. The role of crowd members is carefully calibrated. Recruits are generally actors, who are expected be enthusiastic, but not so zealous as to risk arrest. Critically, they must look and sound authentic. "They almost always hold signs and chant, and sometimes talk to media on behalf of the event," says Swart. Employees also sign non-disclosure forms that protect the client's anonymity, to avoid the embarrassment of their paying for support coming to light.