when signing in there is a guest user icon.

have you turned on "find My Mac?

if so, this is the "Bait" for the person who steals your Mac to log in, and thereby give away their location. It does not allow any access to your files, and does not decrypt your disk, if encrypted.

No.

You leave it on and you ignore that Guest User, because that guest user is going to get the Macbook thief to log in and disclose their location, so you can know where your computer is and get it back.

The discussion in progress was about Find My Mac, and the Guest user it presents.

There is no way to add that guest user AFTER your MacBook is stolen. If it were not present, there is no way to log on, there is no way to get your Mac to report its location to "Find My Mac".

If you want to know where the thief took your MacBook AFTER your Mac is stolen, leave that Guest user sitting there and ignore it. It is a completely separate User. it should have a blank password, and it has NO ACCESS to any of your files.

What?!!

My computer isn't stolen. Why is this guest user with a strange icon, and a password that is unknown to me on my start up screen.

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¿what was their resolution?