One of the main concepts behind the graphic is the stigma of prostitution. The finger to the mouth simply shows the secretive nature behind the sex work industry, reflecting societal ideas that engaging in the industry is shameful and should be treated with discretion. However the stigma behind prostitution often allows sex workers and their rights to be marginalized as they often face physical and verbal abuse, as well as public discrimination.

For more information see this article: https://www.socialconnectedness.org/the-stigmatization-behind-sex-work/