Can I write on roll labels?

It depends on the stock. Uncoated papers, like semi-gloss paper without lamination and textured felt stocks, take a ballpoint pen easily. Permanent markers work on every stock, including laminated labels, if you let the ink dry completely.

Gel pens, other ink pens and pencils may not write on most labels. If writing on them matters, like for dates or batch numbers, test your pen on a sample first.