Did you sign anything at joining which stated your role, salary, and/or office location?

Usually when you get a job offer you'll be sent an offer letter stating role, salary, start date, etc. Often companies ask you to sign it when you accept the offer, but those letters always include language explicitly stating that they don't constitute an employment contract.

you have never signed anything when starting a job?

I mean of course, starting a new job involves signing tons of paperwork. Employee agreements, IT security policies, sometimes codes of conduct or confidentiality agreements... but no contract.