Epson Endeavor - Manual (Page 29)

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.
Note
Some program diskettes have no switch or notch so they are
permanently write-protected. This protects them from being
accidentally erased or altered.
Using Your Computer
1-13