栃木 52 そ 1539

I'm not sure when exactly "栃木 52" was issued, but considering the upper digits went from 2 digits (like we see here) to 3 digits (current issue) only 4 months in to the sales of the S15 Silvia, I have a feeling it's more likely this is a "without vehicle" plate. I'm not entirely sure though, so don't quote me on that.

+1