Epson Progression U12 - Manual (Page 31)

Write-protecting Diskettes
You can write-protect a diskette to prevent its data from being
altered. When a diskette is write-protected, you can read it and
copy data from it, but you cannot store new data on it or delete
any files it contains.
To write-protect a 5.25-inch diskette, cover the small,
rectangular notch (shown below) with an adhesive
write-protect tab. Write-protect tabs usually are included in a
new package of blank 5.25-inch diskettes.
To remove the write protection, peel off the write-protect tab.
1-12 Using Your Computer