Found it. Note the "No Parking for Mt. Sac Students" sign and the plant.
http://goo.gl/maps/ncSt
The first thing I noticed was how far back the limit line is for the stop sign. You did stop at the limit line, correct?
I do think they could have added a "no left turn" sign on the post on the island that contains the stay right graphic for SE bound, no U turn for NE bound, and "one way" for traffic coming out of the residential area opposite of the strip mall.

