Command + Option (Mac) / Control + Alt (Win) + K will enable the painting tool in the Library module. For those of you not familiar with the Painting tool, it allows you to pick an attribute (such as keywords, labels, ratings, target collection etc.) and apply to images by clicking on the image thumbnail in the Grid view. Option (Mac) / Alt (Win) -click with the Painter tool will remove the information. When finished, tapping the Escape key will put the tool away.
I thought that you had to click on each image with the Painter tool in order to apply its “attribute”. However, you can also drag across multiple thumbnails with the Painter Tool in Lightroom to spray them all at once.