Unfortunately, there isn't a direct way to create custom show/hide dropdown arrows for data validation in Excel. The built-in functionality offers a limited appearance for the dropdown indicator.

However, there are a couple of workarounds you can consider to achieve a similar effect:

Workaround 1: Using a Wingdings Symbol (Simpler)

1. Select the cell next to your data validation cell: This cell will act as a placeholder for the custom dropdown icon.
2. Insert Wingdings Symbol: Go to the "Insert" tab and click the "Symbol" button.
3. Choose Wingdings 3 font: Select "Wingdings 3" from the "Font" dropdown menu.
4. Find the down arrow symbol: Locate and choose the down arrow symbol (typically character code 128 or letter "q").
5. Format the symbol cell: Adjust the font size, color, and fill color of the symbol cell to create a subtle dropdown arrow appearance. You can also add a border for a more defined look.
6. Optional: Add Input Message: Go to the "Data" tab and click "Data Validation." In the "Input Message" tab, check the box for "Show input message when cell is selected" and type a message like "Select the previous cell to activate the dropdown" to guide users.

Workaround 2: Using a Macro (More Complex)

This approach involves creating a macro to simulate a dropdown functionality. It requires some knowledge of VBA (Visual Basic for Applications).

1. Record a Macro: Start by recording a macro that activates the dropdown list in the data validation cell.
2. Assign Macro to an Image: Insert an image that resembles a dropdown arrow. Assign the recorded macro to this image so clicking the image triggers the dropdown activation.
3. Conditional Formatting (Optional): You can use conditional formatting to hide the image when the data validation cell is selected, creating the illusion of a disappearing arrow.

Important Note: Both methods have limitations. The Wingdings symbol approach offers a visual cue but doesn't truly hide the standard dropdown arrow. The macro approach involves more complexity and may not be suitable for all users.

Recommendation:

For most cases, the Wingdings symbol workaround might be a sufficient and easier solution. If you need a more dynamic and hidden arrow functionality, consider consulting resources on VBA programming in Excel to create a custom macro solution.