Yes, this is art. IMNSHO Art is anything that was done on purpose but wasn't necessary. As a result you almost can't help but to produce art. Singing in the shower? Art. Snoring in your sleep? Not art. Recording yourself snoring in your sleep? Art again. Of course whether it's good art is a matter of opinion.

As far as I know, everyone is an artist and everything can be considered art.

The trick is to state that fact early enough, when people start questioning your work.

For that matter, how is this "fake"? It's a real sign and is designed to help drivers by giving them accurate information.

It purports to be official, even though it isn't.

Much like a fake Van Gogh painting is still a painting, just not a Van Gogh painting.