To signal is to take an action or actions for the purpose of communicating something other than the literal meaning of the act. Humans and many other animals participate in signaling, often to communicate their own value.
Many social norms, which exist ostensibly for one purpose, in fact exist for a different purpose or purposes that are not stated outwardly. People and organizations participating in signaling may not want to overtly state that they are doing so, because stating that might impair the signaling.
The reasons that people give as why they claim to do things can therefore be misleading. This is not necessarily intentional. People have the tendency to self-delude about their actual intentions (cognitive dissonance).
Generosity: Generosity displays high status, because it portrays the person as charitable and as having spare resources. For this reason, many supposedly altruistic positions are fiercely competitive. Most people prefer to give to community causes (sports groups, local religious organizations, and so on). People prefer to give in ways that make them feel like they can participate (partaking food drives over giving money). Further, people are more inclined to give when whey are being watched, being asked to give, or thinking about mating. All of these things indicate that charity is a form of social signaling.
Body language: Body language can, among other things, convey who has status in the environment. We are unconsciously displaying and negotiating relative status by partaking in body language.
Laughter: If you pay close attention to when people laugh in social interactions, it is usually not because of something actually funny or even a joke. People laugh more frequently in social situations, and more when talking then listening. Laughter is considered a "play signal."
Conversation: Superficially, the point of conversation is only to transfer information. But the way that many conversations flow would not make sense if that were the case. Actually, the point is for the participants to portray themselves as pro-social and knowledgable.
Religion: One of the benefits of a religion is group bonding. For this reason, many religious practices have the partial function of signaling allegiance to the religious group. Religious practices that are particularly demanding weed out people who are not truly committed; this is also part of skin in the game.
Art: We value art that is original, difficult to make, and made by famous individuals. Art has a signaling capability: we participate in art worlds to admire competent people, demonstrating our discerning ability, and flaunt wealth.
Education: Ostensibly, the purpose of an education is learning. In fact, the main reason people are motivated to go to prestigious universities is the signaling ability of a diploma. The fact that one earned a diploma is an indicator of their status. This is something well-studied by economics and game theory. Universities outwardly say that their value comes from the learning, not the signaling, because it would be politically incorrect to admit that their value comes from exclusion.
Politics: People think of themselves as rational voters, capable of logically evaluating issues. For many people, this is not the case. Rather, voters simply adopt the platform of the social tribe they want to align with. This would explain, in part, why people adopt sets of positions, rather than evaluating each issue independently.
Others: there are many other fields where signaling is considered to play a major role, such as consumption and healthcare