I think this refers to proof of address - see below link. You have to go to the police in the area where you live to have your address certified. The term 'invitado' is also used to show the link , or lack of, between a policeman or lawyer and a witness in a trial, for example. Or it can be used just to mean the applicant - something like references to support a bureaucratic process such as getting a job, often for foreign nationals entering a country.