Final answer:
The visibility of the Design tab is an indication that a user is working inside a table in Excel. This tab contains specific tools for table customization and appears when a table cell is selected.
Step-by-step explanation:
When working inside a table in Excel, one of the signs that a user can look for is the visibility of the Design tab. This tab appears on the ribbon automatically when a cell within an Excel table is selected. It contains tools and options specifically for designing and modifying the table, such as table styles, options to add rows or columns, and many other features. The visibility of this tab is a clear indicator that the user is actively working within a table. It's important to note that the table won't be highlighted by 'marching ants,' and Excel will not display a message indicating you are in a table. These options are not standard behaviors of Excel when interacting with tables.