It should be impossible to install it the wrong way, every cpu I've seen has had the pins arranged so they fit in the socket only one way.
Looks like an LGA 2011 socket, and strangely Wikipedia has images of a matching cpu's contacts and they do appear very similar when flipped 180 degrees... except for the corner arrow
But Wikipedia says:
These protrusions, also known as ILM keying, have differently placed protrusions which are intended to mate with cutouts in CPU packagings. These protrusions, also known as ILM keying, have the purpose of preventing installation of incompatible CPUs into otherwise physically compatible sockets, and preventing ILMs to be mounted with a 180-degree rotation relative to the CPU socket.[9]
So I'm assuming if it closes, it's in correctly. And I'm confident it wouldn't boot to the BIOS if it weren't in correctly anyway.
(You could worry more about not getting the heatsink & paste on correctly)
Also, as Mokubai says in his comment below (if it were an answer I'd upvote it, if it becomes one I still will):
the pinouts for CPUs are not rotationally symmetric: cdn.overclock.net/e/ed/eda12cf1_pins_clark4mfk.png if you'd put it in the wrong way it would not have worked at all. You would have a lot of power and ground pins where data lines were meant to be and could have potentially destroyed the CPU. – Mokubai♦ Jan 19 at 16:11
That seems too important to leave the pinout image not see like this:
So it does appear impossible to spin it and still have it working at all.
