^

Writing in IF names in an item's description is as easy as writing a reply, really (like Kistune Mask or Hidden Blade). A notable "good" example for crediting others is the Demon Wings's OP post, on the bottom right.
Keep in mind that some event-based items include credits for original designers, like the Box items or the Cowboy Hat.
Overall there has been some cases where IFs and designers were credited, but idunno if it's necessary to do so in every item/set release (for specific and/or irritating reasons).
If it's really needed to know who did what item, you could start a new thread where you reference each Item Forger and item they made. Sorta like the list of current artists or that one thread about every single item name and their perspective IDs.