My first impression, given the height of the deposits, was that maybe someone had walked their dog there and allowed / encouraged it to urinate on the monument.
http://www.google.com/search?hl=en&q=Oily+urine
“maybe someone had walked their dog there and allowed / encouraged it to urinate on the monument”
That was my first impression also. The height of the “markings” offer no other conclusion. And, yes, dog urine feels oily.