I don't think it's any cause for concern unless you see this fluid leaking on a regular basis. There were a couple of times this winter when my car had been parked in very deep snow that I came out, moved it a short distance, and noticed that the car had deposited the same fluorescent yellow liquid underneath where the engine had been. This first time this happened was in our parking lot at work, and I was only concerned until other people also started pulling out of their parking spots and under at least half of them, all different makes and models, was the same small yellow patch. Something about driving through or parking in snow deep enough to put upward pressure on the underside of the engine bay apparently causes some cars to leak a small amount of what I assume is coolant. Based on my experience with this I would say that it probably was really coming from the front of your car, not the back.
