I think the difference is that the one in Finland can still be entered like a normal tunnel. The deep borehole is literally just a vertical shaft that goes 5-6km down, you put the waste on the bottom and fill it back up. No geological process is bringing the waste back up in any conceivable timescale, and even if the entire civilization collapsed no primitive society can dig to 5km depth, so there's no need for much long lasting signage, no one is going to stumble upon it by accident.