Thank you for your reply, Slide!
It looks you have 2 issues in your post. First is how to make the apostrophe invisible. The second is how to make the cell as a string when there is a hypen at the begining of a cell.
For the first issue, since you don't need to display the apostrophe, why do you put it at the begining. In Excel, the apostrophe at the begining while force the cell to display as a string and the apostrophe is invisible because it works like a command.
The correct way here is to set the cell to string. Moreover, you don't need the apostrophe anymore in your cell value. So Slide is correct!
For the second issue, it's also a feature of Excel. When you input a hypen manually to the cell, it will force the cell to become a formula. However, it looks I cannot reproduce your issue with the following code:
HSSFSheet sheet1 = hssfworkbook.CreateSheet("Sheet1");
sheet1.CreateRow(0).CreateCell(0).SetCellValue("-This is a Sample");
The cell will still display as "-This is a Sample".
Let me know what's your case.