Help Solve the Multi-State, Yellow-Man-in-Road Mystery

When I was living in Manhattan I noticed there were these "things" that someone had created in the road.  They are hooded figures...or maybe better described as Halloween-like ghouls.  Just what are they?  More interestingly...who is putting them in both NYC and Philadelphia?

These catch my attention when I'm walking for obvious reasons. When I saw this one in NYC, I thought "I've seen these in Philadelphia!!"  This particular one is on the West side of the  intersection of Park Ave (or 3rd?) and 24th (or 25th?) St.  If you walk North on the West side of Park Ave (or 3rd?), you will see others at the next few intersections.  (I really wish I had done this blog entry immediately after I took the picture because now I'm bummed I can't remember the exact location.)  I think I may have seen one in white instead of the typical yellow.  (I thought I took other pictures but apparently I didn't because this is the only one I found on my photo card.)

I couldn't wait to get back to Philadelphia and start my new job because I knew exactly where one of these "things" was - on Broad and Juniper Streets.  I use to pass it several times a week when I went out for lunch.  Shortly after I started my job I scurried to that intersection but was foiled.  The road looked (relatively) newly paved.  While I was certainly disappointed, I suspected that eventually I would stumble upon another "thing" somewhere in the city.

Last Thursday, I was crossing the very wide intersection of 15th and Market in Center City Philadelphia and there it was!  I risked life and limb taking this picture.  I was excited.  I finally found one!  Notice how this one looks slightly different - the "knees" are different than its NYC brother and its arms are straighter.

Next time I get back to NYC for a visit I will re-trace my Park Ave (or 3rd?) and 20-something Street steps to see exactly how many figures I find and take photos of them.  In the meantime, I am left wondering.  Who is doing this?  Is it one person, or more?  What does this mean?  Are they done late at night so no one sees or does the "perpetrator" not care if someone watches? 

I need help solving this mystery.  I hope someone can shed some light.  For the next blog entry, I'll show and describe another "something-embedded-in-the-road" mystery.  It's not as mysterious, however, because I've been able to track down more information on that one.