Is this some kind of weird contractor shorthand or something else?

That looks exactly like a shorthand circuit list or a material tally from a panicked apprentice trying to wrap up a rough-in before the inspector showed up the next morning. When you're pulling wire in an old house, especially before digital notes were a thing, we used to scribble wierd grids on scrap paper to track which home runs were pulled to which rooms. Those vertical strokes are likely just a tally for the number of outlets or light boxes tied to a specific breaker.

I've seen guys use their own weird geometric codes for three-way switches versus standard poles beacuse it was faster than writing it out in the dark. It’s common to find these tucked into headers or stuffed into the back of gang boxes because they just get forgotten once the drywall goes up. If the house is realy old, it coud even be a map for where they hid a junction box behind the plaster—a huge no-no by modern code, but somethig people did all the time back then to save on copper. But honestly, if the markings look way too deliberate and don't correlate with the electrical layout, you’re probably looking at a **protective sigil** or some kind of folk magic charm. It was a huge tradition in certain communities to hide 'spirit traps' or 'witch marks' over door frames and window sills to keep bad luck out of the house. People would draw these unique, interlocking symbols that only made sense to them and tuck them away during construction as a way to bless the threshold.

Don't let it stress you out. wether it's a forgotten grocery list for wire nuts or a 50-year-old protection spell, it’s just part of the house's history now. Just toss it back in or throw it away; it’s not going to affect your wiring or your luck. If you’re really curious, check the nearby outlets to see if the 'tally' matches the number of devices on that circuit. That’ll tell you pretty quickly if it’s a **work note** or something more esoteric.

Forget the folk magic theories. That's almost certainly a layout map for a multi-gang setup, probaly for some old Bryant or Hubbell 4-way switches. If the grid has 'X' marks, they were likely mapping out the bridge wires for a complicated traveler system before the plasterers came in. I pulled a similar scrap out of a Victorian last year right next to a run of 12-gauge AC cable. Check if those strokes align with the stud spacing; back then, they’d mark the exact spot to notch the header for a tight fit. If you find any ceramic insulators or a stray Ideal 72B wire nut, you've got your answer on the era.

Spot on with the traveler system theory. I’ve seen these 'maps' tucked into headers specifically when the apprentice didn't have a label maker and was terrified of crossing the neutrals on a shared circuit. One detail folks ussually miss is that those vertical strokes often represent the 'staple count' for the inspector to see how many supports were used in the blind space before the lath went up. If those marks are grouped in threes, it’s a dead giveaway he was tracking his romex staples to make sure he didn't run out before the end of the shift.

Honestly, check if those marks line up with the floor joists or studs. I've found stuff like that where it wasn't about the wiring at all, but a shim map. If the header was out of plumb, a carpenter might've scribbled a 'cheat sheet' for where to pack it out so the trim would actually sit flush. If the marks don't match the circuits, you're probably just looking at some guy's old notes on how to fix a wonky door frame.

This is all way over my head, but the 'spirit trap' thing acutally sounds cooler than a shim map. I’m just a DIY newbie, so I have to ask—if it realy is a map for a hidden junction box like someone mentioned, is that dangerous? I don't want to just shove it back in if there's a live wire buried in the plaster that I might hit later. How woud I even check for that without tearing the whole wall down? All these symbols just look like gibberish to me.

Quick update—you guys were right about the traveler system. I traced the wires back to a junction box in the ceiling and the grid perfectly matched the 4-way switch layout mentioned. It definately looks like a panicked apprentice’s cheat sheet to avoid crossing neutrals. Glad it’s not some wierd curse! Thanks for the help, saved me alot of head-scratching.