If you are pretty sure it is silver, then it just means that it is 83.5% sterling instead of the more typical 92.5% with the 925 stamp. It is sometimes referred to as British Silver or European. I am not sure though what the other components are that make up the other....pause, need to do the math.......16.5% of it. I believe it is safe and I have never heard of anyone using lead in it. It's just got a little less silver and a wee bit more alloy material.
The 835 mark can be on any metal, even platinum or gold, but that is not as common as it is to be found on silver. It just means it is 83.5% silver or gold or platinum.
Hopefully others will chime in to help ease your mind about wearing it. I would wear it without worry, if it were me.