Some birds feed by hanging upside down. There are "sock" style thistle seed feeders for goldfinches designed for the birds to be able to hang any which way. Nuthatches and some warblers also move around tree trunks and branches upside down as naturally as they do right side up. I came across these feeders on Amazon that feature images of birds eating upside down. Some are natural. Not all of them, though...
I ran across this Perky-Pet feeder. It looks pretty straightforward, but the Tufted Titmouse on the left side seems to be having trouble using the feeder. It's perched upside down with its beak nowhere near a food port. Maybe it's just playing?
Like I said, there are birds that will naturally feed while hanging or standing upside down. Take, for instance, the clip art nuthatch on this feeder. This kind of feeder is mesh all around, giving complete access to the seed. Old-school, regular-perching birds can use the perches on the bottom, while nuthatches can swoop in an get a seed from wherever.
Then there are bird feeders designed so the patrons have to hang upside down on them, like this feeder for finches. Rather than having a mesh surface like the feeder above, or using cloth sock-style material, this is a clear, solid cylinder feeder with ports for the nyger, or thistle, seed. The perches are arranged below the ports so any bird who wants to get at the seed is obliged to hang upside-down.
Repost of article first published 01/11/2012