Traps? That looks like a blink trap. But I think I have seen some that were just art and nothing more too. Step on it and learn!
"Most" of them? Well that's scary. I've tried stepping on them a few times but as far as I can see it does nothing.
The ones that freak me out are the ones that look like metal grates formed of red-hot molten metal. Avoided those things for ages before a zoo finally forced me to step on one, and nothing happened :S
And someday, someone (FAAAAAAX!) will create a trap that will look just like that, for added paranoia factor.
I would not be one bit surprised if he already has made some and is waiting to bundle it with VoM or FAXPAX without telling us. I really liked his not-quite Grog traps...
They usually appear on the 10th floor and in mysterious portals (i've seen one on the 3rd floor) and they do nothing. Nothing, that is, until Fax sees this thread...
Fax already has traps looking like this in his Vaults of Evil Destruction Utter Annihilation Candy Maslech.