About triangle indicators in cells
From Microsoft Office Excel 2003
About triangle indicators in cells
Triangles in the corners of cells in Microsoft Excel indicate formula errors, comments, or smart tag options.
A green triangle in the upper-left corner of a cell indicates an error in the formula in the cell. If you select the cell, Trace Error
appears. Click the arrow next to the button for a list of options.
Note The color of the error checking triangle indicator can be changed by clicking Options on the Tools menu, and then clicking the Error Checking tab.
A red triangle in the upper-right corner of a cell indicates a comment in the cell. If you rest the mouse cursor over the triangle, you can view the text of the comment.
A purple triangle in the lower-right corner of a cell indicates a smart tag. If you rest the mouse cursor over the triangle, Smart Tag Actions appears. Click the arrow next to the button for a list of smart tag options.