A friend of mine works at Quincy University in Illinois, and has said that recently a few marks looking like this have shown up around campus. Can anyone help identify them (and possibly put some security fears to rest)?
A one-eyed cat.
Martini.
It’s a secret code referring to the Martini-Enfield rifle, reminding people that Australia confiscated people’s guns, and a warning to beware of gun control measures.
And if I’m making that up, may I win the jackpot in the lottery.
Looks possibly like a modified question mark.
Also, might want to ask a Hash House Harrier, since they occasionally cause alarm when their symbols are found. (They mark their improvised running trails with flour or chalk which people sometimes mistake for arsenic or drugs or weird terrorist gang symbols. But it’s just a weekly running game they play.)
Edit: Not seeing that particular symbol in a google image search for HHH trail markings though.
I think maybe it is utility workers surveying marks.
Surveyors generally use stakes, flags, chisel marks, and pins. Utilities are usually marked with straight lines, and they use spray paint or flags rather than chalk.
I don’t know, but I have seen arrows and straight lines were gas lines may be buried, painted with spray paint, close to new construction.
Does it indicate an alien landing site?
It resembles some of those Aztec space port thingies.
It definitely made me think of Martini before anything else, and I had no knowledge of the rifle of the background story with Australia.
It looks sort of like a combination of the Deathly Hallows symbol and the Joker’s question mark.
A two-beaked duck.
A martini makes you into a boob who questions things. 
If there was a cross on the bottom stroke I’d say it would be a damn fine symbol for the women’s march movement. (It’s not)
Yeah. Lines and arrows and maybe initials or numbers. The color of the spray paint can indicate the type of utility underground.
My theory is that it’s warning of a nearby C.H.U.D. lair.
Seriously? Someone has ‘security fears’ because strange chalk symbols are appearing in an area where there’s a huge concentration of 19-22 year-olds with too much time on their hands and beginnings of an education?
Tell them that, so far, the Harvard Bridge has survived fifty years, despite its mysterious markings, and they can probably stop worrying.
Well correct me if I wrong, but don’t terrorist alway mark the location of their next target weeks in advance? They wouldn’t want a bomb going off to be a surprise for goodness sake!
I’d like to nominate this for Post of the Week.
I second the nomination.
Can’t tell if he’s entering a room or leaving.