Manufacturers fill pens with ink designed to go on a surface permanently. When the ink inadvertently gets on a surface such as a tie, you need to take care of it immediately or you will have a pen-stained tie, permanently. Silk fibres are strong but you don't want to chemically treat them or you might change or weaken the protein structure of the fibres.
Fold a towel and place on a flat surface. Lay a couple of paper towels over the towel. Place the tie on top face down and cover it with a couple more paper towels. Place a heavy weight on top of the stain to absorb any extra ink.
Dissolve the ink by working an alcohol-based product, such as aftershave, hairspray, rubbing alcohol or even vodka, into the surface of the tie. Dip a cotton swab in the solvent and wipe the ink spot, working from the outer edge to the centre. Change the swab every time you see ink on the fibres so you don't end up spreading the ink.
Rinse off the solvent with a rag dipped in warm water. Tamp the area lightly to remove any residue.
Check the label on the tie to see what type of cleaning the makers recommend. Take the tie to a professional cleaning service if the label requires it.