The image above is a Klan membership application form. It dates from the 1920s. The organisation would send them out unsolicited to people who’d been recommended for membership by a friend or associate who was already a Klansman.
Even today one apparently still fills out an application in order to join. Though according to Slate’s Brian Palmer:
The Klan application has undergone some telling changes. The KKK was acutely concerned about immigrants in the 1920s, and the application used to ask whether the prospective member’s parents were born in the United States and whether the applicant believed in “the principles of a PURE Americanism.” Few of today’s applications ask about the applicant’s birthplace, let alone that of his parents. Religion also appears to have been a greater focus. Pre-Depression applicants had to answer a series of questions about religion, such as “Are you a gentile or Jew?” “Of what church are you a member (if any)?” and “Of what religious faith are your parents?”
Palmer goes onto suggest that the Klan has relatively lax membership standards and that the application process is mostly an excuse to charge membership fees ($20 apparently). More sophisticated hate groups will run criminal records and credit checks in order to try and detect undercover police officers trying to infiltrate them.