Signifiers communicate where the action should take place, it is an important communication device to the recipient whether or not the communication is intended.
Signifiers signal things, in particular, what actions are possible and how they should be done. They must be perceivable, else they fail to function.
Signifier refers to any mark or sound, any perceivable indicator that communicates appropriate behavior to a person.
People search for clues for signs that help them understand it is the sign that is important, anything that might signify meaningful information.
Designers need to provide signifiers, Good design requires, among other things, good communication of the purpose, structure, and operation of the device to the people who use it.
That is the role of the signifier.
Information from: The design of everyday things, Signifiers Pg13.
Social signifiers are those that are relevant to social usages. Some social indicators simply are the unintended but informative result of the behavior of others.
A social signifier is one that is either created or interpreted by people or society, signifying social activity or appropriate social behavior.