A good friend of mine, now over 70 years old who was a successful art seller and gallerist
sees signing on the front as plain vanity and suggests to simply sign on the backside with a pencil.
Graphite is quite archival ....
I think you can see it different ways,
but the artistic value of something is not raised by writing your name on the front of it.
Exception might be if your signature is a calligraphic piece of art each time taking at least 2 hours to make ...
Market value - no idea.
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 ... "
So - it depends on your clients and if it helps you to sell, if that is the main goal.
I am not selling art, but when I give a print away as a present I sign with a soft pencil on the backside of the print.
Even when mounted and my signature therefore is invisible.