Informal Social Controls.
Like their formal counterpart, informal controls exist to reward or punish people for acceptable / unacceptable behaviour (what sociologists call deviance). Informal controls cover a vast array of possible sanctions and tend to differ from individual to individual, group to group and society to society. Informal controls apply to informal norms of behaviour and they include things like ridicule, sarcasm, disapproving looks, punching people in the face and so forth.
For example, at a Women's Institute gathering a disapproving look may be enough to tell you that people think it is not appropriate to flirt with the vicar. Amongst members of a criminal gang, however, it is unlikely that a disapproving look would be used as a means of informal social control should you tell them you intend to inform on their activities to the police.