How to add a custom mark to the product when making an additional purchase

Retired Boards Appdev Metafields
1

Hello everyone, I have a question：

How to add a custom mark to the product when making an additional purchase (the mark is different for each user) and save it in the order after placing the order

Use metafields? Is there a better solution？

2

Hey @azhe

Would a line item property suffice? If not can you please elaborate on the custom mark?