Have you tried Micron pens? They're said to be permanent. I've used to make quilt labels. Fine lines, no blobbing on the fabric, legible. They come in a variety of colours.

Try Sharpie "Rub-A-Dub" Laundry Marker.

Made for going through the laundry, washer and dry cleaning.

No. I haven't. I searched Amazon & they only come in dark colors which doesn't help me with the dark t-shirts. I will try will the lighter t-shirts. Anyone suggestions what to do with the black & dark navy t shirts? Needs a color that will show up against the dark fabric.

With any type pen, I found it helps to set the ink with a hot dry iron afterward. I did some tests, a few years ago, ( I think with a Sharpie but can't swear to it since it was 18 years go) and the sample that was heat-set did not fade as much.

My mother is in an Alzheimer's care facility, and I mark her clothing on the labels with a Sharpie. The labels are usually a light color.

When my kids were younger and in sports, I bought a silver Sharpie pen to write their names on their uniforms. It worked. I washed their uniforms in warm water at the time since they were dark colors--usually dark blue or black. If it wears off, you can re-write the names on the articles as needed. You'll be keeping an eye on the status of the ink as you launder the items, so you will know when a touch-up is needed.

The silver is paint. :)

He's not too old for an iron-on with his name--just put it on the inside. :)

The most popular marker that you can use for fabric is the Sharpie permanent fabric marker. You can also use the Arteza fabric markers, Crayola fabric markers, Shuttle Art 36 colors fabric markers. You can also use fabric paint to set the permanent markers on the fabric.

Sew in some short strips of colored ribbon...red, green. Seal the cut ends of the ribbon with Fray Check.