To be able to delete your signup if needed, you must be using the same device/ browser/ connection/ cookie as then.
Hover over long names to see all of them. They are cut off to fit the box.
You can click the [x] next to yor name to delete it.
If using a shared public computer (library, etc), uncheck 'Make delete-able on this device' When filling in the signup form. If you do this, others (and you) will not be able to delete your signup.