A side lever safety or a side lever? For some unknown reason, Pieper came out with a side lever shortly before his death in 1898. He even filed a patent on it. Why he took this "backwards step" is unknown. The side lever had seen it's hey day and better designs were around.

The gun you saw was produced in the 1890's. There are a few of them around, though not commonly seen. In the condition you describe, at best it only worth $200 - $300.

Pete