"Allah Wakbar" looks like a native Arabic speaker who is not too familiar with English attempting to render "Allahu akbar."
"NYPD Probes 'Allah' Graffiti at WTC Memorial," by Michael King for WNBC New York, June 28 (thanks to Mackie):
NEW YORK -- The NYPD Hate Crimes Task Force is investigating after the words "Allah Wakbar" were found written on a granite seat at the Sept. 11 memorial on Tuesday, law enforcement sources tell NBC 4 New York.
A private custodian cleaning the area found the graffiti, written in pink and black marker, on a seat in the plaza area between the north and south pools around 10:30 p.m. Tuesday.
Investigators believe someone wrote the words that day. No incidents were reported on Tuesday, and the area is not in the view of any security cameras.
After cops were called, the words were removed by a power washer, sources said. The rest of the memorial was inspected, but no other graffiti was found....