Final answer:
The sure sign of working within a table in Excel is the ability to sort and filter data, as this feature is enhanced for table structures.
Step-by-step explanation:
The sign that a user is working inside a table in Excel is the ability to sort and filter data. While Excel does show gridlines and provide options for merging cells and using formulas and functions. However, these features are not exclusive to tables. In contrast, Excel offers additional functionalities for sorting and filtering when data is organized within a table structure. Users can tell they are working with a table if extra tabs appear in the Ribbon, such as 'Table Design' and 'Table Tools', offering options such as predefined table styles, the insertion of rows/columns, and features to remove duplicates or convert the table back to a range.
The presence of gridlines is a sign that a user is working inside a table in Excel. Gridlines are the horizontal and vertical lines that define the boundaries of each cell in a table. They help in visually organizing the data in Excel.
While the other options mentioned in the question are also available in Excel, they are not exclusive to working inside a table. Sorting and filtering data, merging cells, and using formulas and functions can be done outside of a table as well.