Swamped

"Look at that wall!"

There's a marking, and it's glowing. That's odd - you definitely should have noticed it before.

"Looks a bit like a rune." You turn to Marian. "You're a wizard, you could probably say that for sure."

"Not a rune, not that I'm familiar with anyhow," she replies. "But I think I've seen it."

She pulls out her sketchpad.

"I put the map together quickly, so I didn't draw the symbols in detail. But there are distinct ones at each spot, and I'm pretty sure this is the marking I saw here. Let me see the map again to be sure."

You show it to her. She nods.

"Why's it showing up now, though? I took out the glow-lamp earlier and I would have seen a rune when I was looking around..."

You glance at the lamp in your hands.

"Or does this one give off different light somehow? It was in a side room. Could have been put there intentionally so those in the know could see the symbol."

Drip glances at the shattered glass on the ground.

"You may be correct. The two lanterns appear to have different types of glow-moss."

"Well, we don't need to go to all the crypts if we want the symbols, since it seems Matilda left us a full list," Marian says. She's sketching frantically. "Since these seem more important than I first thought, I'll put them down properly now. Maybe a second look at the pattern with the symbols in place will suggest something to one of you."

She finishes, and shows off the new map, now with a complete set of symbols. You look over it, and you realize something.