Returning Expensive Headphones

I found very expensive headphones on the bus. I was afraid to hand them over to the lost and found department, fearing that they might keep them for themselves. I advertised this in every possible way to find the owner, but I couldn't. What should I do now?

Dear …!
In most cases, headphones don’t have any distinguishing marks. Things such as their brand name or color, and anything that is done by the company that makes them, as well as the bus route, are not considered identifying signs. Therefore, the letter of the law is that the headphones belong to you. Making an effort to return them to their owner is an act of piety.
However, if there is a unique sign unrelated to the production of the headphones, there is an absolute obligation to return them. It is advisable to contact the lost and found department to check if anyone has reported these headphones missing.
After making reasonable efforts, you may keep the headphones for yourself and write down their value on a note. If in the future the owner turns up, you should return their monetary value to him.

Shulchan Aruch (Choshen Mishpat, Siman 262).