Its a modern disease, even creators of simple T-Shirts put their name on the front of their "pieces of art" ....
Everything is "art" today.
If there is a lot of hype, hybris, buzz, whatever around the person of the artist / the brand,
people might actually want to have a mark on the front, to be able to show it:
"See - I have this 20,000 $$ Feldhaim street shot 5x7" limited edition hanging on my wall ... "
I suppose one has to mention the obvious artist who old sold one painting whilst alive, yet now his works sell for absurdly large sums.
It's very hard to say what will become valuable in the future