If this is a seriously prized signature, here's what you do: scan it, isolate the signature in GIMP (or Photoshop if you're into that sort of thing), and send your phone to a laser engraver who can permanently fix the design in place. Then wash off the original. As a side bonus, you can get the same thing done on future phones in perpetuity.

META: It's successful posts like these that show that Rule 5 of this community is misguided.

People want to ask and answer these types of "How do I...?" questions. There are no negative comments here. It adds value and activity to the community. They should be allowed.

Rule 5 should be changed.

Clean the area carefully (you want to remove existing dirt and skin oils without damaging the autograph any further).

Mask the area off with painters tape.

Spray with 3 thin coats of spray polyurethane from the hardware store.

Give it a couple days to completely cure before handling it.

A spray fixative should do it. You can get it at an art supply store. I had a similar thing on glass and it worked great… but for display, not something going in and out of your pocket. Is that the actual phone or a case? Either way if the autograph is important to you its now a display piece.

Resin or hard coat prob. Make sure you cover up anything you don't want coated in goo

Probably clear coat it.
It sounds barbaric but probably nail polish could work also in a pinch.
Then put on a seethrough case.

Get a new phone case and keep this one sealed in a clear box

Go to an auto parts store and get some spray clear coat! Do a few layers

I studied paper conservation so this is technically out of my wheelhouse. But while I was doing my MA we had an external tutor come in and demonstrate how to conserve various synthetic paints. The problem you're having is the pigment has become friable as the solvent has evaporated. It may be possible to replace some of that lost solvent by exposing the signature to the right solvent in a gas chamber (stuff that you should leave to a professional conservator that works in this medium). The signature will still be susceptible to being abraded off so a cover would be needed. Preferably one that doesn't contact the signature.

Professional conservation work is not cheap so you'd need to get a quote and judge if it is worth it to you.

It looks like the solvent from the ink has stained the case which will be more permanent than the friable pigment. You could just accept that the pigment is going to fall off and live with the signature's underlying stain (though you'd still probably be wise to put a clear case on the phone to reduce the abrasion caused by handing and pocket storage). Be aware that the stain may become less recognisable with age (like an old tattoo) as the solvent spreads on the case.

If you are keen to try to fix it yourself the most important thing to do is get your hands on the exact same marker and a similar substrate as the phone body to test any proposed solutions. Give any test time to show itself. I relabeled thousands of books in an archive with a permanent archival pen then put adhesive clear covers over them, after five years none of those labels are readable anymore as the solvent in the adhesive made the ink spread. They were fine while I still worked there but I was getting some stink eye when I paid visit those five years later.

I may end up just buying a new phone, TBH.

remotelove@lemmy.ca

I got answers here but you'll need to do a little leg work.

First off, get a good guess at what the marker is. If it's permanent ink, it's probably using alcohol base, if it's acrylic it's water, etc. Depending on the solvent used in the marker you can pick a coating material that won't damage the original markings. You're going to want it in spray can form unless you own an airbrush.

If all else fails, someone else pointed out automotive clear coat. That will do fine if you follow the info carefully.

Once you have a clear coat that either does or preferably doesn't react with the mark, you're going to tape off your phone. Masking tape is fine, I find washi tape from the scap booking section to work better. It sticks tighter but peals back up easily and without residues. Go around the camera hump, over the surface, around the outside, and completely cover the screen. Always do more than you think is necessary, because it's easier to waste tape than remove paint.

Now for the best results you're going to want a hot, dry, windless environment. If it's not like that outside you can do it indors with ventilation, just lay down and old sheet and open some windows.

Now your clear coat is going to be in a spray can. Look around the tip for a mark on the can, that will indicate the angle of the intake. Point the sprayer the same direction and test it a few times on cardboard until you have a good and steady stream. Practice the next part if you have any doubts about yourself. Just cut a piece of cardboard that's phone sized and pretend you're doing the real thing.

You're going to start each spray off to the side of the target. The initial push and your ability to move is not perfect even after years of doing this and will lead to a wet spot. Make sure that spot is on the work area and not the piece. Steadily move across the piece and end the spray on the work area again, this prevents splatter.

You're going to gently dust the phone in coat. Adjust to the next pass and do it again. Then let this coat dry completely not tacky, not dull, full dry.

Turn the phone 90 degrees and do it again. You're going to repeat this process 30 or 40 times. Eventually it will build up into one solid coating across the entire surface. Ideally you let that cure for 24 hour.

This is your phone so I understand if that's not doable, just make sure to ler each coat dry.

I mean, taking a high quality picture of it, like this, is a great way.

Satan?

Hydrogel or glass back protector? I'm not sure what happens when you remove those though. But you might not need to

Couldn't you use a sheet of plastic they use for fingerprints in order to at least transfer it?

A screen protection coating but on the back. Maybe first do a test on another phone

I wonder if it would be possible to remove that part of the case and find another?