Q uses a Tripcode on the Q board(s) on 8ch. It gets updated once in awhile and verified by the board-owner (codemonkey for 8ch).   Only Q has that password/code which allows users to see who it is.  The sites like Qanon.pub & Qanonposts use that tripcode to find & post them automatically.  Most imageboards and 2channel-style discussion boards allow (and encourage) anonymous posting and use a system of tripcodes instead of registration. A tripcode is the hashed result of a password that allows one's identity to be recognized without storing any data about users.