If it's real silver, then it shouldn't be attracted to magnets. Post a screenshot if you can.
Could be silver plate, with the underneath being stainless steel.
If there aren't any makers marks then it probably isn't real silver.
Chances are that a maker wouldn't put their marks on a part of it which can easily fall off.
For the moral view, you should probably hand it in to the police as lost and found.
I don't know what your specific laws are, but in some places, if lost and found is collected in a certain amount of time then it gets returned to whoever found it.