When people are unsure how to behave, they rely on social cues for guidance. In 2006, Mathew Salganik conducted an online experiment that demonstrated how the musical preferences of over 14,000 participants were manipulated by making certain songs appear more popular than others.
Not only did these artificial signals change which songs participants liked, they also created polarisation between "popular" and "unpopular" music that closely resembled the real-world music industry.
A comparable field test designed by Robert Cialdini and Noah Goldstein found that hotel guests reused their towels more often when it was presented as "normal" behaviour than they did when asked on environmental grounds. Compared to a sign reading "Help save the environment", an alternative that announced "The majority of guests in this room reuse their towels" increased towel reuse by 32.5%.
The influence of social signals on behaviour has also been applied to charity donations. In 2012, the Behavioural Insights Team worked alongside cooperative legal services to try and increase charitable giving in wills. One ("plain ask") group of clients were presented with a simple question during their will-writing session:
"Would you like to leave any money to charity in your will?"
A second ("social norm") group received a similar question, this time framed using social signals:
"Many of our customers like to leave money to charity in their will. Are there any causes you're passionate about?"
Although the "plain ask" group chose to leave a gift far more often than clients who were not asked directly (choosing to donate 10.8% of the time), the second group were far more generous. Not only did 15.4% of the "social norm" group choose to donate, but the donations were themselves significantly larger.
Donation platforms like JustGiving and GoFundMe incorporate a range of social signals that encourage generosity. For example, fundraisers are asked to suggest a target amount when they build their page. This target communicates expectations to the fundraiser's social circle and the percentage score clearly shows whether it is living up to these hopes. In their guidelines for fundraisers, JustGiving suggests that providing a target value can increase the amount a page raises by 46%.

Alongside the target value, a typical JustGiving page also features a board with the names of previous donors. Showing these past donations helps create a feeling of consensus, especially if the visitor identifies with prior donors. It also creates an environment where social comparison makes a clear minimum on the size of donations.