|Zinnia of the Compositae family|
On herbs it is hard to miss the seeds as they tend to be obvious, like on dill or basil. But flowering herbs like Nasturtiums are a bit harder to locate.
Alliums, or chives, are a flowering bulb, but the attractive puff ball flowers do produce seeds as well. You want to cut the flowers before they drop, but after they seem spent. If you wait too long the seed will scatter before you collect the flower head.