So I’m watching an episode of my new favorite TV show, “The Librarians,” which is about a D&D adventuring party ….

(Oh, wait, I’m sorry — it’s really about these “librarians” — who fight bad magic on the side of good with John Laroquette offering sage advice from the sidelines.)

And in this episode they need to make a pentagram to ward off the magic of that nameless sorceress from Arthurian Britain (hope that isn’t too spoilery).

But hey, this is the modern world! How do you make a pentagram? Well, one of the librarians, armed with blue duct tape, paces the length out on the floor and uses the tape to denote the points of the star.

Well, I thought it was cool.

Anyway, the point is that the blue duct tape reminded me about chalk lines and how they can be one of those things that denote — even for nonarcanists in a party — the presence or use of magic.

For the GM, it can be useful when you need a party to recognize that magic is going on here. Chalk lines left behind denote a warding circle or a summoning charm — or even that most magical of magic — guidelines for magical engineering. (You don’t think those freemasons, long suspected of being spellcasters and secret-keepers, were creating buildings with trigonometry and geometry, did you?)

Wouldn’t it be cool for one of the PCs to be able to enter a room, and with the panache of a Sherlock Holmes, announce that this was the site of a magical battle?

“Well, see here. This circular chalk line indicates a magical ward, and where the line was scuffed indicates where the field was breached, and the scorch marks on the far wall, in a reverse silhouette of an orc’s head is a flame spell and these other spell components scattered about, they also represent spells cast hurriedly, as if in battle. It’s really quite elementary.”

Well, maybe that’s overdoing it a bit. (Those blood splatters on the floor were pretty telling, too). But having PCs recognize chalk as a telltale sign of magic can have its advantages. It’s a clue on the trail to the big evil one’s lair. It also tells them to prepare their own spellcasters, keying them in on what spells they might need to counter.

And nothing’s better than a chalk scrawl to say: “Watch your magical step! Big ley line right here!”

So, don’t forget to keep some chalk dust in your GM’s kit. You never know when you’ll need to sprinkle some out and leave a sign for your players.

*Achoo!*

Did I forget to mention I’m allergic to chalk dust? Oh well.