You sign once when you connect, and that sign-in covers social actions such as posts, follows and comments for 30 days. You also sign for actions that move money or change something on chain: buying, selling, creating a coin, buying Boosts or UpVotes, signing up as a recruiter and claiming rewards.
A sign-in message is not a transaction and cannot move your coins. Still, read each prompt. If a prompt appears that you did not trigger, close it.