Previously, previously, previously, previously, previously, previously, previously.
-_- where in SF is this, by chance?
The linked website refers to "Curtain Road", which I believe is in London.
For the stalkers: https://firstname.lastname@example.org,-0.0803716,3a,43.6y,273.98h,88.89t/data=!3m6!1e1!3m4!1sJBce8f7GLnC-85nxaeXGfg!2e0!7i13312!8i6656
There are smaller and slightly less sinister spikes on the sills of that fancy building across from the Stud bar, along 9th, also south west corner of Potrero and 15th. I used to work in the area and there are a bunch of places around there with window spikes, but mostly to prevent sitting/leaning, I don't recall that I've seen them in areas big enough to lie down in.
Well, "don't sleep here" is definitely what this one is (Tenderloin), but a very common occurrence in SF is benches that have "arm rests" that just happen to make it impossible to lie down.
I find it hilarious that it is always the landlords who are blamed for defensive architecture. That's easy as long as you are not the shop owner who fears to lose customers (so he doesn't land on the street himself); but in fact, it is the fault of society on the whole, and should be seen as such.
I hope that mattress is very heavy, so it's hard to remove.