I saw one a few years back on the W&P/P&W in Amity, OR. Of course this was part of the SP local lines which Portland & Western/Willamette & Pacific took over long before UP took over SP, and not narrow gauge. I think they were quite common in Oregon on the SP.
We have been offered one by ODOT, for display purposes only since they are no longer allowed for new installations. There was talk about installing it in Sumpter next to the sidewalk leading into the Dredge Heritage State Park just before the SVRy crossing. That crossing is already approved and protected by lights and bells.
dan