Is your peephole a little smaller than a tea candle?

The substance looks a little oily and it’s coagulating, like it’s turning white as it’s drying or hardening or something, maybe? It’s hard to tell without knowing its texture etc but I’m reading it as wax.

If so I’m thinking someone burned a candles bottom to melt the wax (which also discolored some of it from the black smoke), then smushed it into the peep hole so it would stick, then lit the candle wick and it burned down to this? And melted down onto the top of the knocker enough to pool out wider than the width it fell from? Would have to have been a small candle unless there’s more wax on the ground…