According to Kashrus Magazine, the OU (Orthodox Union) has now started using a “DE” symbol in limited situations for products that use dairy equipment and cannot contain actual dairy ingredients. This DE symbol is only used for a limited number of products.
According to the OUKOSHER website:
An ‘OU-D’ symbol indicates:
The product is a Kosher dairy product.
The product contains a dairy ingredient or a dairy derivative.
Alternatively, the product, while not containing dairy ingredients itself, was made on equipment also used for making dairy products.