These messaging boards allow you to create "accounts" in the form of a name and a password. Many people could create accounts with the name Q and pose as Q, yes, however the real Q is identified through his trip code. The trip code is the letters and numbers you see next to Qs name on the research boards that are assigned based on the password the user created. So even though anyone could name themselves Q, the only real one will be the one with the trip code that is generated from the password Q assigns. Hes changed his tripcode a few times as he moves boards, and he always confirms them with the previous trip code account before moving onto the next one.