To me it seems like a data validation input message.
To remove it, go to the data tab, select data validation, then there is a tab in the middle named 'input message' and unselect 'show input message when cell is selected'.
To me it seems like a data validation input message.
To remove it, go to the data tab, select data validation, then there is a tab in the middle named 'input message' and unselect 'show input message when cell is selected'.